diff --git a/spec/compiler/interpreter/primitives_spec.cr b/spec/compiler/interpreter/primitives_spec.cr
index 5a9f4c856952..21aad383a01c 100644
--- a/spec/compiler/interpreter/primitives_spec.cr
+++ b/spec/compiler/interpreter/primitives_spec.cr
@@ -316,7 +316,7 @@ describe Crystal::Repl::Interpreter do
       assert_overflows 1_i16 + 32767
       assert_overflows 1_u32 + 4294967295
       assert_overflows 1_i32 + 2147483647
-      assert_overflows 1_u64 + 18446744073709551615
+      assert_overflows 1_u64 + 18446744073709551615u64
       assert_overflows 1_i64 + 9223372036854775807
     end
 
@@ -328,7 +328,7 @@ describe Crystal::Repl::Interpreter do
       assert_overflows 1_u32 - 2
       assert_overflows 1_i32 - 2147483650
       assert_overflows 1_u64 - 2
-      assert_overflows 1_i64 - 9223372036854775810
+      assert_overflows 1_i64 - 9223372036854775810u64
     end
 
     context "*" do
diff --git a/spec/compiler/macro/macro_methods_spec.cr b/spec/compiler/macro/macro_methods_spec.cr
index eaa712936b83..7d949ae0932b 100644
--- a/spec/compiler/macro/macro_methods_spec.cr
+++ b/spec/compiler/macro/macro_methods_spec.cr
@@ -2949,6 +2949,10 @@ module Crystal
           assert_macro %({{parse_type :Foo }}), %(nil)
         end
       end
+
+      it "exposes syntax warnings" do
+        assert_warning %({% parse_type "Foo(0x8000_0000_0000_0000)" %}), "Warning: 0x8000_0000_0000_0000 doesn't fit in an Int64, try using the suffix u64 or i128"
+      end
     end
 
     describe "printing" do
diff --git a/spec/compiler/parser/warnings_spec.cr b/spec/compiler/parser/warnings_spec.cr
new file mode 100644
index 000000000000..2bfb4ff937bc
--- /dev/null
+++ b/spec/compiler/parser/warnings_spec.cr
@@ -0,0 +1,30 @@
+require "../../support/syntax"
+
+private def assert_parser_warning(source, message, *, file = __FILE__, line = __LINE__)
+  parser = Parser.new(source)
+  parser.filename = "/foo/bar/baz.cr"
+  node = parser.parse
+
+  warnings = parser.warnings.infos
+  warnings.size.should eq(1), file: file, line: line
+  warnings[0].should contain(message), file: file, line: line
+end
+
+describe "Parser warnings" do
+  it "warns on suffix-less UInt64 literals > Int64::MAX" do
+    values = [
+      "9223372036854775808", # Int64::MAX + 1
+      "9999999999999999999",
+      "10000000000000000000",
+      "18446744073709551615", # UInt64::MAX
+      "0x8000_0000_0000_0000",
+      "0xFFFF_FFFF_FFFF_FFFF",
+    ]
+
+    values.each do |value|
+      assert_parser_warning value, "Warning: #{value} doesn't fit in an Int64, try using the suffix u64 or i128"
+      assert_parser_warning "Foo(#{value})", "Warning: #{value} doesn't fit in an Int64, try using the suffix u64 or i128"
+      assert_parser_warning "{{ #{value} }}", "Warning: #{value} doesn't fit in an Int64, try using the suffix u64 or i128"
+    end
+  end
+end
diff --git a/spec/compiler/semantic/warnings_spec.cr b/spec/compiler/semantic/warnings_spec.cr
index fb0a915431ab..91634f95e1ec 100644
--- a/spec/compiler/semantic/warnings_spec.cr
+++ b/spec/compiler/semantic/warnings_spec.cr
@@ -761,4 +761,12 @@ describe "Semantic: warnings" do
         CR
     end
   end
+
+  it "exposes syntax warnings" do
+    assert_warning UInt64::MAX.to_s, "Warning: #{UInt64::MAX} doesn't fit in an Int64, try using the suffix u64 or i128"
+  end
+
+  it "exposes syntax warnings after macro interpolation" do
+    assert_warning "{% begin %}0x8000_0000_0000_000{{ 0 }}{% end %}", "Warning: 0x8000_0000_0000_0000 doesn't fit in an Int64, try using the suffix u64 or i128"
+  end
 end
diff --git a/spec/spec_helper.cr b/spec/spec_helper.cr
index 9bf1b0ca05bb..69e3566e73e0 100644
--- a/spec/spec_helper.cr
+++ b/spec/spec_helper.cr
@@ -48,9 +48,10 @@ def assert_type(str, *, inject_primitives = false, flags = nil, file = __FILE__,
 end
 
 def semantic(code : String, wants_doc = false, inject_primitives = false, flags = nil, filename = nil)
-  node = parse(code, wants_doc: wants_doc, filename: filename)
+  warnings = WarningCollection.new
+  node = parse(code, wants_doc: wants_doc, filename: filename, warnings: warnings)
   node = inject_primitives(node) if inject_primitives
-  semantic node, wants_doc: wants_doc, flags: flags
+  semantic node, warnings: warnings, wants_doc: wants_doc, flags: flags
 end
 
 private def inject_primitives(node : ASTNode)
@@ -66,8 +67,9 @@ private def inject_primitives(node : ASTNode)
   end
 end
 
-def semantic(node : ASTNode, wants_doc = false, flags = nil)
+def semantic(node : ASTNode, *, warnings = nil, wants_doc = false, flags = nil)
   program = new_program
+  program.warnings = warnings if warnings
   program.flags.concat(flags.split) if flags
   program.wants_doc = wants_doc
   node = program.normalize node
@@ -139,7 +141,7 @@ end
 def assert_warning(code, message, *, file = __FILE__, line = __LINE__)
   warning_failures = warnings_result(code)
   warning_failures.size.should eq(1), file: file, line: line
-  warning_failures[0].should start_with(message), file: file, line: line
+  warning_failures[0].should contain(message), file: file, line: line
 end
 
 def assert_macro(macro_body, expected, args = nil, *, expected_pragmas = nil, flags = nil, file = __FILE__, line = __LINE__)
diff --git a/spec/std/big/big_int_spec.cr b/spec/std/big/big_int_spec.cr
index 1069e069af61..4aa7aaadcd6a 100644
--- a/spec/std/big/big_int_spec.cr
+++ b/spec/std/big/big_int_spec.cr
@@ -504,12 +504,12 @@ describe "BigInt" do
       big = BigInt.new("9" * 32)
       expect_raises(OverflowError) { big.to_i64 }
       expect_raises(OverflowError) { big.to_u64 }
-      big.to_i64!.should eq(-8814407033341083649) # 99999999999999999999999999999999 - 5421010862428*(2**64)
-      big.to_u64!.should eq(9632337040368467967)  # 99999999999999999999999999999999 - 5421010862427*(2**64)
+      big.to_i64!.should eq(-8814407033341083649)   # 99999999999999999999999999999999 - 5421010862428*(2**64)
+      big.to_u64!.should eq(9632337040368467967u64) # 99999999999999999999999999999999 - 5421010862427*(2**64)
     end
 
     it "between 63 and 64 bits" do
-      big = BigInt.new(i = 9999999999999999999)
+      big = BigInt.new(i = 9999999999999999999u64)
       expect_raises(OverflowError) { big.to_i64 }
       big.to_u64.should eq(i)
       big.to_i64!.should eq(-8446744073709551617) # 9999999999999999999 - 2**64
@@ -529,7 +529,7 @@ describe "BigInt" do
       big.to_i64.should eq(i)
       expect_raises(OverflowError) { big.to_u64 }
       big.to_i64!.should eq(i)
-      big.to_u64!.should eq(18446744073709541617) # -9999 + 2**64
+      big.to_u64!.should eq(18446744073709541617u64) # -9999 + 2**64
     end
 
     it "negative between 32 and 63 bits" do
@@ -537,7 +537,7 @@ describe "BigInt" do
       big.to_i64.should eq(i)
       expect_raises(OverflowError) { big.to_u64 }
       big.to_i64!.should eq(i)
-      big.to_u64!.should eq(18446734073709551617) # -9999999999999 + 2**64
+      big.to_u64!.should eq(18446734073709551617u64) # -9999999999999 + 2**64
     end
 
     it "negative between 63 and 64 bits" do
@@ -552,8 +552,8 @@ describe "BigInt" do
       big = BigInt.new("-" + "9" * 20)
       expect_raises(OverflowError) { big.to_i64 }
       expect_raises(OverflowError) { big.to_u64 }
-      big.to_i64!.should eq(-7766279631452241919) # -9999999999999999999 + 5*(2**64)
-      big.to_u64!.should eq(10680464442257309697) # -9999999999999999999 + 6*(2**64)
+      big.to_i64!.should eq(-7766279631452241919)    # -9999999999999999999 + 5*(2**64)
+      big.to_u64!.should eq(10680464442257309697u64) # -9999999999999999999 + 6*(2**64)
 
       big = BigInt.new("-" + "9" * 32)
       expect_raises(OverflowError) { big.to_i64 }
diff --git a/spec/std/crystal/compiler_rt/ashlti3_spec.cr b/spec/std/crystal/compiler_rt/ashlti3_spec.cr
index 45176e801c59..2fe1780c2279 100644
--- a/spec/std/crystal/compiler_rt/ashlti3_spec.cr
+++ b/spec/std/crystal/compiler_rt/ashlti3_spec.cr
@@ -5,40 +5,40 @@ require "./spec_helper"
 # Ported from https://github.com/llvm/llvm-project/blob/ce59ccd04023cab3a837da14079ca2dcbfebb70c/compiler-rt/test/builtins/Unit/ashlti3_test.c
 
 it ".__ashlti3" do
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 0).should eq make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 1).should eq make_ti(0xFDB97530ECA8642B, 0xFDB97530ECA8642A)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 2).should eq make_ti(0xFB72EA61D950C857, 0xFB72EA61D950C854)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 3).should eq make_ti(0xF6E5D4C3B2A190AF, 0xF6E5D4C3B2A190A8)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 4).should eq make_ti(0xEDCBA9876543215F, 0xEDCBA98765432150)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 28).should eq make_ti(0x876543215FEDCBA9, 0x8765432150000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 29).should eq make_ti(0x0ECA8642BFDB9753, 0x0ECA8642A0000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 30).should eq make_ti(0x1D950C857FB72EA6, 0x1D950C8540000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 31).should eq make_ti(0x3B2A190AFF6E5D4C, 0x3B2A190A80000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 32).should eq make_ti(0x76543215FEDCBA98, 0x7654321500000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 33).should eq make_ti(0xECA8642BFDB97530, 0xECA8642A00000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 34).should eq make_ti(0xD950C857FB72EA61, 0xD950C85400000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 35).should eq make_ti(0xB2A190AFF6E5D4C3, 0xB2A190A800000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 36).should eq make_ti(0x6543215FEDCBA987, 0x6543215000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 60).should eq make_ti(0x5FEDCBA987654321, 0x5000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 61).should eq make_ti(0xBFDB97530ECA8642, 0xA000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 62).should eq make_ti(0x7FB72EA61D950C85, 0x4000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 63).should eq make_ti(0xFF6E5D4C3B2A190A, 0x8000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 64).should eq make_ti(0xFEDCBA9876543215, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 65).should eq make_ti(0xFDB97530ECA8642A, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 66).should eq make_ti(0xFB72EA61D950C854, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 67).should eq make_ti(0xF6E5D4C3B2A190A8, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 68).should eq make_ti(0xEDCBA98765432150, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 92).should eq make_ti(0x8765432150000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 93).should eq make_ti(0x0ECA8642A0000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 94).should eq make_ti(0x1D950C8540000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 95).should eq make_ti(0x3B2A190A80000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 96).should eq make_ti(0x7654321500000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 97).should eq make_ti(0xECA8642A00000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 98).should eq make_ti(0xD950C85400000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 99).should eq make_ti(0xB2A190A800000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 100).should eq make_ti(0x6543215000000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 124).should eq make_ti(0x5000000000000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 125).should eq make_ti(0xA000000000000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 126).should eq make_ti(0x4000000000000000, 0x0000000000000000)
-  __ashlti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 127).should eq make_ti(0x8000000000000000, 0x0000000000000000)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 0).should eq make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 1).should eq make_ti(0xFDB97530ECA8642Bu64, 0xFDB97530ECA8642Au64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 2).should eq make_ti(0xFB72EA61D950C857u64, 0xFB72EA61D950C854u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 3).should eq make_ti(0xF6E5D4C3B2A190AFu64, 0xF6E5D4C3B2A190A8u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 4).should eq make_ti(0xEDCBA9876543215Fu64, 0xEDCBA98765432150u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 28).should eq make_ti(0x876543215FEDCBA9u64, 0x8765432150000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 29).should eq make_ti(0x0ECA8642BFDB9753u64, 0x0ECA8642A0000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 30).should eq make_ti(0x1D950C857FB72EA6u64, 0x1D950C8540000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 31).should eq make_ti(0x3B2A190AFF6E5D4Cu64, 0x3B2A190A80000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 32).should eq make_ti(0x76543215FEDCBA98u64, 0x7654321500000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 33).should eq make_ti(0xECA8642BFDB97530u64, 0xECA8642A00000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 34).should eq make_ti(0xD950C857FB72EA61u64, 0xD950C85400000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 35).should eq make_ti(0xB2A190AFF6E5D4C3u64, 0xB2A190A800000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 36).should eq make_ti(0x6543215FEDCBA987u64, 0x6543215000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 60).should eq make_ti(0x5FEDCBA987654321u64, 0x5000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 61).should eq make_ti(0xBFDB97530ECA8642u64, 0xA000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 62).should eq make_ti(0x7FB72EA61D950C85u64, 0x4000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 63).should eq make_ti(0xFF6E5D4C3B2A190Au64, 0x8000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 64).should eq make_ti(0xFEDCBA9876543215u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 65).should eq make_ti(0xFDB97530ECA8642Au64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 66).should eq make_ti(0xFB72EA61D950C854u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 67).should eq make_ti(0xF6E5D4C3B2A190A8u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 68).should eq make_ti(0xEDCBA98765432150u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 92).should eq make_ti(0x8765432150000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 93).should eq make_ti(0x0ECA8642A0000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 94).should eq make_ti(0x1D950C8540000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 95).should eq make_ti(0x3B2A190A80000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 96).should eq make_ti(0x7654321500000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 97).should eq make_ti(0xECA8642A00000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 98).should eq make_ti(0xD950C85400000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 99).should eq make_ti(0xB2A190A800000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 100).should eq make_ti(0x6543215000000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 124).should eq make_ti(0x5000000000000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 125).should eq make_ti(0xA000000000000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 126).should eq make_ti(0x4000000000000000u64, 0x0000000000000000u64)
+  __ashlti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 127).should eq make_ti(0x8000000000000000u64, 0x0000000000000000u64)
 end
diff --git a/spec/std/crystal/compiler_rt/ashrti3_spec.cr b/spec/std/crystal/compiler_rt/ashrti3_spec.cr
index 6d593ff7918c..716892eca731 100644
--- a/spec/std/crystal/compiler_rt/ashrti3_spec.cr
+++ b/spec/std/crystal/compiler_rt/ashrti3_spec.cr
@@ -5,40 +5,40 @@ require "./spec_helper"
 # Ported from https://github.com/llvm/llvm-project/blob/ce59ccd04023cab3a837da14079ca2dcbfebb70c/compiler-rt/test/builtins/Unit/ashrti3_test.c
 
 it ".__ashrti3" do
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 0).should eq make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 1).should eq make_ti(0xFF6E5D4C3B2A190A, 0xFF6E5D4C3B2A190A)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 2).should eq make_ti(0xFFB72EA61D950C85, 0x7FB72EA61D950C85)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 3).should eq make_ti(0xFFDB97530ECA8642, 0xBFDB97530ECA8642)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 4).should eq make_ti(0xFFEDCBA987654321, 0x5FEDCBA987654321)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 28).should eq make_ti(0xFFFFFFFFEDCBA987, 0x6543215FEDCBA987)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 29).should eq make_ti(0xFFFFFFFFF6E5D4C3, 0xB2A190AFF6E5D4C3)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 30).should eq make_ti(0xFFFFFFFFFB72EA61, 0xD950C857FB72EA61)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 31).should eq make_ti(0xFFFFFFFFFDB97530, 0xECA8642BFDB97530)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 32).should eq make_ti(0xFFFFFFFFFEDCBA98, 0x76543215FEDCBA98)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 33).should eq make_ti(0xFFFFFFFFFF6E5D4C, 0x3B2A190AFF6E5D4C)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 34).should eq make_ti(0xFFFFFFFFFFB72EA6, 0x1D950C857FB72EA6)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 35).should eq make_ti(0xFFFFFFFFFFDB9753, 0x0ECA8642BFDB9753)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 36).should eq make_ti(0xFFFFFFFFFFEDCBA9, 0x876543215FEDCBA9)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 60).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xEDCBA9876543215F)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 61).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xF6E5D4C3B2A190AF)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 62).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFB72EA61D950C857)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 63).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFDB97530ECA8642B)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 64).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFEDCBA9876543215)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 65).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFF6E5D4C3B2A190A)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 66).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFB72EA61D950C85)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 67).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFDB97530ECA8642)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 68).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFEDCBA987654321)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 92).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFEDCBA987)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 93).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFF6E5D4C3)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 94).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFB72EA61)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 95).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFDB97530)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 96).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFEDCBA98)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 97).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFF6E5D4C)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 98).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFB72EA6)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 99).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFDB9753)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 100).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFEDCBA9)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 124).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 125).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 126).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF)
-  __ashrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 127).should eq make_ti(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 0).should eq make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 1).should eq make_ti(0xFF6E5D4C3B2A190Au64, 0xFF6E5D4C3B2A190Au64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 2).should eq make_ti(0xFFB72EA61D950C85u64, 0x7FB72EA61D950C85u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 3).should eq make_ti(0xFFDB97530ECA8642u64, 0xBFDB97530ECA8642u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 4).should eq make_ti(0xFFEDCBA987654321u64, 0x5FEDCBA987654321u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 28).should eq make_ti(0xFFFFFFFFEDCBA987u64, 0x6543215FEDCBA987u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 29).should eq make_ti(0xFFFFFFFFF6E5D4C3u64, 0xB2A190AFF6E5D4C3u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 30).should eq make_ti(0xFFFFFFFFFB72EA61u64, 0xD950C857FB72EA61u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 31).should eq make_ti(0xFFFFFFFFFDB97530u64, 0xECA8642BFDB97530u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 32).should eq make_ti(0xFFFFFFFFFEDCBA98u64, 0x76543215FEDCBA98u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 33).should eq make_ti(0xFFFFFFFFFF6E5D4Cu64, 0x3B2A190AFF6E5D4Cu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 34).should eq make_ti(0xFFFFFFFFFFB72EA6u64, 0x1D950C857FB72EA6u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 35).should eq make_ti(0xFFFFFFFFFFDB9753u64, 0x0ECA8642BFDB9753u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 36).should eq make_ti(0xFFFFFFFFFFEDCBA9u64, 0x876543215FEDCBA9u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 60).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xEDCBA9876543215Fu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 61).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xF6E5D4C3B2A190AFu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 62).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFB72EA61D950C857u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 63).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFDB97530ECA8642Bu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 64).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFEDCBA9876543215u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 65).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFF6E5D4C3B2A190Au64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 66).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFB72EA61D950C85u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 67).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFDB97530ECA8642u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 68).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFEDCBA987654321u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 92).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFEDCBA987u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 93).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFF6E5D4C3u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 94).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFB72EA61u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 95).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFDB97530u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 96).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFEDCBA98u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 97).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFF6E5D4Cu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 98).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFB72EA6u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 99).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFDB9753u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 100).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFEDCBA9u64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 124).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 125).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 126).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64)
+  __ashrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 127).should eq make_ti(0xFFFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64)
 end
diff --git a/spec/std/crystal/compiler_rt/divmod128_spec.cr b/spec/std/crystal/compiler_rt/divmod128_spec.cr
index 88746f873138..db87bc46057e 100644
--- a/spec/std/crystal/compiler_rt/divmod128_spec.cr
+++ b/spec/std/crystal/compiler_rt/divmod128_spec.cr
@@ -68,16 +68,16 @@ describe "__udivti3" do
   test__udivti3(0, 1, 0)
   test__udivti3(2, 1, 2)
 
-  test__udivti3(make_tu(0x0, 0x8000000000000000), 1, make_tu(0x0, 0x8000000000000000))
-  test__udivti3(make_tu(0x0, 0x8000000000000000), 2, make_tu(0x0, 0x4000000000000000))
-  test__udivti3(make_tu(0xffffffffffffffff, 0xffffffffffffffff), 2, make_tu(0x7fffffffffffffff, 0xffffffffffffffff))
+  test__udivti3(make_tu(0x0, 0x8000000000000000u64), 1, make_tu(0x0, 0x8000000000000000u64))
+  test__udivti3(make_tu(0x0, 0x8000000000000000u64), 2, make_tu(0x0, 0x4000000000000000u64))
+  test__udivti3(make_tu(0xffffffffffffffffu64, 0xffffffffffffffffu64), 2, make_tu(0x7fffffffffffffffu64, 0xffffffffffffffffu64))
 end
 
 describe "__umodti3" do
   test__umodti3(0, 1, 0)
   test__umodti3(2, 1, 0)
 
-  test__umodti3(make_tu(0x0, 0x8000000000000000), 1, 0)
-  test__umodti3(make_tu(0x0, 0x8000000000000000), 2, 0)
-  test__umodti3(make_tu(0xffffffffffffffff, 0xffffffffffffffff), 2, 1)
+  test__umodti3(make_tu(0x0, 0x8000000000000000u64), 1, 0)
+  test__umodti3(make_tu(0x0, 0x8000000000000000u64), 2, 0)
+  test__umodti3(make_tu(0xffffffffffffffffu64, 0xffffffffffffffffu64), 2, 1)
 end
diff --git a/spec/std/crystal/compiler_rt/lshrti3_spec.cr b/spec/std/crystal/compiler_rt/lshrti3_spec.cr
index 61eab9fb4b0c..567e384f37f1 100644
--- a/spec/std/crystal/compiler_rt/lshrti3_spec.cr
+++ b/spec/std/crystal/compiler_rt/lshrti3_spec.cr
@@ -5,40 +5,40 @@ require "./spec_helper"
 # Ported from https://github.com/llvm/llvm-project/blob/ce59ccd04023cab3a837da14079ca2dcbfebb70c/compiler-rt/test/builtins/Unit/lshrti3_test.c
 
 it ".__lshrti3" do
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 0).should eq make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 1).should eq make_ti(0x7F6E5D4C3B2A190A, 0xFF6E5D4C3B2A190A)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 2).should eq make_ti(0x3FB72EA61D950C85, 0x7FB72EA61D950C85)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 3).should eq make_ti(0x1FDB97530ECA8642, 0xBFDB97530ECA8642)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 4).should eq make_ti(0x0FEDCBA987654321, 0x5FEDCBA987654321)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 28).should eq make_ti(0x0000000FEDCBA987, 0x6543215FEDCBA987)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 29).should eq make_ti(0x00000007F6E5D4C3, 0xB2A190AFF6E5D4C3)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 30).should eq make_ti(0x00000003FB72EA61, 0xD950C857FB72EA61)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 31).should eq make_ti(0x00000001FDB97530, 0xECA8642BFDB97530)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 32).should eq make_ti(0x00000000FEDCBA98, 0x76543215FEDCBA98)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 33).should eq make_ti(0x000000007F6E5D4C, 0x3B2A190AFF6E5D4C)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 34).should eq make_ti(0x000000003FB72EA6, 0x1D950C857FB72EA6)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 35).should eq make_ti(0x000000001FDB9753, 0x0ECA8642BFDB9753)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 36).should eq make_ti(0x000000000FEDCBA9, 0x876543215FEDCBA9)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 60).should eq make_ti(0x000000000000000F, 0xEDCBA9876543215F)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 61).should eq make_ti(0x0000000000000007, 0xF6E5D4C3B2A190AF)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 62).should eq make_ti(0x0000000000000003, 0xFB72EA61D950C857)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 63).should eq make_ti(0x0000000000000001, 0xFDB97530ECA8642B)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 64).should eq make_ti(0x0000000000000000, 0xFEDCBA9876543215)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 65).should eq make_ti(0x0000000000000000, 0x7F6E5D4C3B2A190A)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 66).should eq make_ti(0x0000000000000000, 0x3FB72EA61D950C85)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 67).should eq make_ti(0x0000000000000000, 0x1FDB97530ECA8642)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 68).should eq make_ti(0x0000000000000000, 0x0FEDCBA987654321)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 92).should eq make_ti(0x0000000000000000, 0x0000000FEDCBA987)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 93).should eq make_ti(0x0000000000000000, 0x00000007F6E5D4C3)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 94).should eq make_ti(0x0000000000000000, 0x00000003FB72EA61)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 95).should eq make_ti(0x0000000000000000, 0x00000001FDB97530)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 96).should eq make_ti(0x0000000000000000, 0x00000000FEDCBA98)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 97).should eq make_ti(0x0000000000000000, 0x000000007F6E5D4C)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 98).should eq make_ti(0x0000000000000000, 0x000000003FB72EA6)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 99).should eq make_ti(0x0000000000000000, 0x000000001FDB9753)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 100).should eq make_ti(0x0000000000000000, 0x000000000FEDCBA9)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 124).should eq make_ti(0x0000000000000000, 0x000000000000000F)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 125).should eq make_ti(0x0000000000000000, 0x0000000000000007)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 126).should eq make_ti(0x0000000000000000, 0x0000000000000003)
-  __lshrti3(make_ti(0xFEDCBA9876543215, 0xFEDCBA9876543215), 127).should eq make_ti(0x0000000000000000, 0x0000000000000001)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 0).should eq make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 1).should eq make_ti(0x7F6E5D4C3B2A190Au64, 0xFF6E5D4C3B2A190Au64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 2).should eq make_ti(0x3FB72EA61D950C85u64, 0x7FB72EA61D950C85u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 3).should eq make_ti(0x1FDB97530ECA8642u64, 0xBFDB97530ECA8642u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 4).should eq make_ti(0x0FEDCBA987654321u64, 0x5FEDCBA987654321u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 28).should eq make_ti(0x0000000FEDCBA987u64, 0x6543215FEDCBA987u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 29).should eq make_ti(0x00000007F6E5D4C3u64, 0xB2A190AFF6E5D4C3u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 30).should eq make_ti(0x00000003FB72EA61u64, 0xD950C857FB72EA61u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 31).should eq make_ti(0x00000001FDB97530u64, 0xECA8642BFDB97530u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 32).should eq make_ti(0x00000000FEDCBA98u64, 0x76543215FEDCBA98u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 33).should eq make_ti(0x000000007F6E5D4Cu64, 0x3B2A190AFF6E5D4Cu64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 34).should eq make_ti(0x000000003FB72EA6u64, 0x1D950C857FB72EA6u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 35).should eq make_ti(0x000000001FDB9753u64, 0x0ECA8642BFDB9753u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 36).should eq make_ti(0x000000000FEDCBA9u64, 0x876543215FEDCBA9u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 60).should eq make_ti(0x000000000000000Fu64, 0xEDCBA9876543215Fu64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 61).should eq make_ti(0x0000000000000007u64, 0xF6E5D4C3B2A190AFu64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 62).should eq make_ti(0x0000000000000003u64, 0xFB72EA61D950C857u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 63).should eq make_ti(0x0000000000000001u64, 0xFDB97530ECA8642Bu64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 64).should eq make_ti(0x0000000000000000u64, 0xFEDCBA9876543215u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 65).should eq make_ti(0x0000000000000000u64, 0x7F6E5D4C3B2A190Au64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 66).should eq make_ti(0x0000000000000000u64, 0x3FB72EA61D950C85u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 67).should eq make_ti(0x0000000000000000u64, 0x1FDB97530ECA8642u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 68).should eq make_ti(0x0000000000000000u64, 0x0FEDCBA987654321u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 92).should eq make_ti(0x0000000000000000u64, 0x0000000FEDCBA987u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 93).should eq make_ti(0x0000000000000000u64, 0x00000007F6E5D4C3u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 94).should eq make_ti(0x0000000000000000u64, 0x00000003FB72EA61u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 95).should eq make_ti(0x0000000000000000u64, 0x00000001FDB97530u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 96).should eq make_ti(0x0000000000000000u64, 0x00000000FEDCBA98u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 97).should eq make_ti(0x0000000000000000u64, 0x000000007F6E5D4Cu64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 98).should eq make_ti(0x0000000000000000u64, 0x000000003FB72EA6u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 99).should eq make_ti(0x0000000000000000u64, 0x000000001FDB9753u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 100).should eq make_ti(0x0000000000000000u64, 0x000000000FEDCBA9u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 124).should eq make_ti(0x0000000000000000u64, 0x000000000000000Fu64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 125).should eq make_ti(0x0000000000000000u64, 0x0000000000000007u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 126).should eq make_ti(0x0000000000000000u64, 0x0000000000000003u64)
+  __lshrti3(make_ti(0xFEDCBA9876543215u64, 0xFEDCBA9876543215u64), 127).should eq make_ti(0x0000000000000000u64, 0x0000000000000001u64)
 end
diff --git a/spec/std/crystal/compiler_rt/mulodi4_spec.cr b/spec/std/crystal/compiler_rt/mulodi4_spec.cr
index be5a57516d23..c723380014e5 100644
--- a/spec/std/crystal/compiler_rt/mulodi4_spec.cr
+++ b/spec/std/crystal/compiler_rt/mulodi4_spec.cr
@@ -13,9 +13,9 @@ private def test__mulodi4(a : Int64, b : Int64, expected : Int64, expected_overf
   end
 end
 
-private HEX_0_7FFFFFFFFFFFFFFF = 0x7FFFFFFFFFFFFFFF.to_i64!
-private HEX_0_8000000000000001 = 0x8000000000000001.to_i64!
-private HEX_0_8000000000000000 = 0x8000000000000000.to_i64!
+private HEX_0_7FFFFFFFFFFFFFFF = 0x7FFFFFFFFFFFFFFFi64
+private HEX_0_8000000000000001 = 0x8000000000000001u64.to_i64!
+private HEX_0_8000000000000000 = 0x8000000000000000u64.to_i64!
 
 describe "__mulodi4" do
   test__mulodi4(0, 0, 0, 0)
diff --git a/spec/std/crystal/compiler_rt/muloti4_spec.cr b/spec/std/crystal/compiler_rt/muloti4_spec.cr
index ed52925ee8f9..62215f73ff95 100644
--- a/spec/std/crystal/compiler_rt/muloti4_spec.cr
+++ b/spec/std/crystal/compiler_rt/muloti4_spec.cr
@@ -50,96 +50,96 @@ describe "__muloti4" do
   test__muloti4(2097152, -4398046511103, -9223372036852678656, 0)
   test__muloti4(-2097152, -4398046511103, 9223372036852678656, 0)
   test__muloti4(make_ti(0x00000000000000B5, 0x04F333F9DE5BE000),
-    make_ti(0x0000000000000000, 0x00B504F333F9DE5B),
-    make_ti(0x7FFFFFFFFFFFF328, 0xDF915DA296E8A000), 0)
-  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
+    make_ti(0x0000000000000000u64, 0x00B504F333F9DE5Bu64),
+    make_ti(0x7FFFFFFFFFFFF328u64, 0xDF915DA296E8A000u64), 0)
+  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
     -2,
-    make_ti(0x8000000000000000, 0x0000000000000001), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 1)
   test__muloti4(-2,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
-    make_ti(0x8000000000000000, 0x0000000000000001), 1)
-  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 1)
+  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
     -1,
-    make_ti(0x8000000000000000, 0x0000000000000001), 0)
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 0)
   test__muloti4(-1,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
-    make_ti(0x8000000000000000, 0x0000000000000001), 0)
-  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 0)
+  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
     0,
     0, 0)
   test__muloti4(0,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
     0, 0)
-  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
+  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
     1,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF), 0)
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64), 0)
   test__muloti4(1,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF), 0)
-  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64), 0)
+  test__muloti4(make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
     2,
-    make_ti(0x8000000000000000, 0x0000000000000001), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 1)
   test__muloti4(2,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF),
-    make_ti(0x8000000000000000, 0x0000000000000001), 1)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000000),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 1)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000000u64),
     -2,
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
   test__muloti4(-2,
-    make_ti(0x8000000000000000, 0x0000000000000000),
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000000),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000000u64),
     -1,
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
   test__muloti4(-1,
-    make_ti(0x8000000000000000, 0x0000000000000000),
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000000),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000000u64),
     0,
     0, 0)
   test__muloti4(0,
-    make_ti(0x8000000000000000, 0x0000000000000000),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64),
     0, 0)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000000),
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000000u64),
     1,
-    make_ti(0x8000000000000000, 0x0000000000000000), 0)
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 0)
   test__muloti4(1,
-    make_ti(0x8000000000000000, 0x0000000000000000),
-    make_ti(0x8000000000000000, 0x0000000000000000), 0)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000000),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 0)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000000u64),
     2,
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
   test__muloti4(2,
-    make_ti(0x8000000000000000, 0x0000000000000000),
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000001),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000001u64),
     -2,
-    make_ti(0x8000000000000000, 0x0000000000000001), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 1)
   test__muloti4(-2,
-    make_ti(0x8000000000000000, 0x0000000000000001),
-    make_ti(0x8000000000000000, 0x0000000000000001), 1)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000001),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 1)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000001u64),
     -1,
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF), 0)
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64), 0)
   test__muloti4(-1,
-    make_ti(0x8000000000000000, 0x0000000000000001),
-    make_ti(0x7FFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF), 0)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000001),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64),
+    make_ti(0x7FFFFFFFFFFFFFFFu64, 0xFFFFFFFFFFFFFFFFu64), 0)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000001u64),
     0,
     0, 0)
   test__muloti4(0,
-    make_ti(0x8000000000000000, 0x0000000000000001),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64),
     0, 0)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000001),
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000001u64),
     1,
-    make_ti(0x8000000000000000, 0x0000000000000001), 0)
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 0)
   test__muloti4(1,
-    make_ti(0x8000000000000000, 0x0000000000000001),
-    make_ti(0x8000000000000000, 0x0000000000000001), 0)
-  test__muloti4(make_ti(0x8000000000000000, 0x0000000000000001),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64), 0)
+  test__muloti4(make_ti(0x8000000000000000u64, 0x0000000000000001u64),
     2,
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
   test__muloti4(2,
-    make_ti(0x8000000000000000, 0x0000000000000001),
-    make_ti(0x8000000000000000, 0x0000000000000000), 1)
+    make_ti(0x8000000000000000u64, 0x0000000000000001u64),
+    make_ti(0x8000000000000000u64, 0x0000000000000000u64), 1)
 end
diff --git a/spec/std/crystal/compiler_rt/multi3_spec.cr b/spec/std/crystal/compiler_rt/multi3_spec.cr
index 7e93e3efce1d..3c3c8eae7070 100644
--- a/spec/std/crystal/compiler_rt/multi3_spec.cr
+++ b/spec/std/crystal/compiler_rt/multi3_spec.cr
@@ -48,5 +48,5 @@ it ".__multi3" do
   __multi3(
     make_ti(0x00000000000000B5, 0x04F333F9DE5BE000),
     make_ti(0x0000000000000000, 0x00B504F333F9DE5B)
-  ).should eq make_ti(0x7FFFFFFFFFFFF328, 0xDF915DA296E8A000)
+  ).should eq make_ti(0x7FFFFFFFFFFFF328u64, 0xDF915DA296E8A000u64)
 end
diff --git a/spec/std/float_printer/diy_fp_spec.cr b/spec/std/float_printer/diy_fp_spec.cr
index 560e4db13e7f..cfaee9de64d0 100644
--- a/spec/std/float_printer/diy_fp_spec.cr
+++ b/spec/std/float_printer/diy_fp_spec.cr
@@ -41,7 +41,7 @@ describe DiyFP do
   end
 
   it "multiply" do
-    fp1 = DiyFP.new(0x8000000000000000, 11)
+    fp1 = DiyFP.new(0x8000000000000000_u64, 11)
     fp2 = DiyFP.new(2_u64, 13)
     prod = fp1 * fp2
 
@@ -163,7 +163,7 @@ describe DiyFP do
 
     fp.exp.should eq -0x3FF - 52 + 1 - 63
     # This is a denormal; so no hidden bit
-    fp.frac.should eq 0x8000000000000000
+    fp.frac.should eq 0x8000000000000000_u64
   end
 
   it "normalizes max f64" do
diff --git a/spec/std/random_spec.cr b/spec/std/random_spec.cr
index 5adb283b3b7c..37b951c89def 100644
--- a/spec/std/random_spec.cr
+++ b/spec/std/random_spec.cr
@@ -180,7 +180,7 @@ describe "Random" do
   it "allows creating a new default random with a seed" do
     values = Array.new(2) do
       rand = Random.new(1234)
-      {rand.rand, rand.rand(0xffffffffffffffff), rand.rand(2), rand.rand(-5i8..5i8)}
+      {rand.rand, rand.rand(0xffffffffffffffffu64), rand.rand(2), rand.rand(-5i8..5i8)}
     end
 
     values[0].should eq values[1]
diff --git a/spec/std/string_spec.cr b/spec/std/string_spec.cr
index 780d5c27a175..55023929d00b 100644
--- a/spec/std/string_spec.cr
+++ b/spec/std/string_spec.cr
@@ -390,12 +390,12 @@ describe "String" do
     end
 
     describe "to_u64" do
-      it { "18446744073709551615".to_u64.should eq(18446744073709551615) }
+      it { "18446744073709551615".to_u64.should eq(18446744073709551615u64) }
       it { "0".to_u64.should eq(0) }
       it { expect_raises(ArgumentError) { "18446744073709551616".to_u64 } }
       it { expect_raises(ArgumentError) { "-1".to_u64 } }
 
-      it { "18446744073709551615".to_u64?.should eq(18446744073709551615) }
+      it { "18446744073709551615".to_u64?.should eq(18446744073709551615u64) }
       it { "18446744073709551616".to_u64?.should be_nil }
       it { "18446744073709551616".to_u64 { 0 }.should eq(0) }
     end
diff --git a/spec/support/syntax.cr b/spec/support/syntax.cr
index 5514fc1d4acf..e1fd8f43d951 100644
--- a/spec/support/syntax.cr
+++ b/spec/support/syntax.cr
@@ -158,8 +158,9 @@ def assert_syntax_error(str, message = nil, line = nil, column = nil, metafile =
   end
 end
 
-def parse(string, wants_doc = false, filename = nil)
-  parser = Parser.new(string)
+def parse(string, wants_doc = false, filename = nil, warnings = nil)
+  parser = Parser.new(string, warnings: warnings)
+  parser.warnings = warnings if warnings
   parser.wants_doc = wants_doc
   if filename
     parser.filename = filename
diff --git a/src/big/big_decimal.cr b/src/big/big_decimal.cr
index 0edabd7c18c4..66945bcc6899 100644
--- a/src/big/big_decimal.cr
+++ b/src/big/big_decimal.cr
@@ -704,7 +704,7 @@ struct Int
   # Converts `self` to `BigDecimal`.
   # ```
   # require "big"
-  # 12123415151254124124.to_big_d
+  # 123456789012345678.to_big_d
   # ```
   def to_big_d : BigDecimal
     BigDecimal.new(self)
diff --git a/src/compiler/crystal/codegen/codegen.cr b/src/compiler/crystal/codegen/codegen.cr
index 1bbf9670bfd7..5dca53131d67 100644
--- a/src/compiler/crystal/codegen/codegen.cr
+++ b/src/compiler/crystal/codegen/codegen.cr
@@ -18,7 +18,7 @@ module Crystal
 
   class Program
     def run(code, filename = nil, debug = Debug::Default)
-      parser = Parser.new(code)
+      parser = new_parser(code)
       parser.filename = filename
       node = parser.parse
       node = normalize node
diff --git a/src/compiler/crystal/command/format.cr b/src/compiler/crystal/command/format.cr
index a4c4bfdab467..76ebe9c3ef34 100644
--- a/src/compiler/crystal/command/format.cr
+++ b/src/compiler/crystal/command/format.cr
@@ -155,7 +155,7 @@ class Crystal::Command
 
     # This method is for mocking `Crystal.format` in test.
     private def format(filename, source)
-      Crystal.format(source, filename: filename)
+      Crystal.format(source, filename: filename, report_warnings: STDERR)
     end
 
     private def error(msg)
diff --git a/src/compiler/crystal/compiler.cr b/src/compiler/crystal/compiler.cr
index 8b402e542fa4..0d99635497a7 100644
--- a/src/compiler/crystal/compiler.cr
+++ b/src/compiler/crystal/compiler.cr
@@ -230,7 +230,7 @@ module Crystal
     end
 
     private def parse(program, source : Source)
-      parser = Parser.new(source.code, program.string_pool)
+      parser = program.new_parser(source.code)
       parser.filename = source.filename
       parser.wants_doc = wants_doc?
       parser.parse
diff --git a/src/compiler/crystal/interpreter/prompt.cr b/src/compiler/crystal/interpreter/prompt.cr
index 6ab6a1bea055..ea6077cc4aa5 100644
--- a/src/compiler/crystal/interpreter/prompt.cr
+++ b/src/compiler/crystal/interpreter/prompt.cr
@@ -78,6 +78,8 @@ class Crystal::Repl::Prompt
       @line_number += 1
       @incomplete = false
 
+      parser.warnings.report(STDOUT)
+
       node
     rescue ex : Crystal::SyntaxException
       # TODO: improve this
diff --git a/src/compiler/crystal/interpreter/repl.cr b/src/compiler/crystal/interpreter/repl.cr
index cb0faa82a2c4..1a07333064a7 100644
--- a/src/compiler/crystal/interpreter/repl.cr
+++ b/src/compiler/crystal/interpreter/repl.cr
@@ -127,9 +127,12 @@ class Crystal::Repl
   end
 
   private def parse_code(code, filename = "")
-    parser = Parser.new code, @program.string_pool
+    warnings = @program.warnings.dup
+    warnings.infos = [] of String
+    parser = Parser.new code, @program.string_pool, warnings: warnings
     parser.filename = filename
     parsed_nodes = parser.parse
+    warnings.report(STDOUT)
     @program.normalize(parsed_nodes, inside_exp: false)
   end
 
diff --git a/src/compiler/crystal/macros/macros.cr b/src/compiler/crystal/macros/macros.cr
index ff5e8064f965..e088f477f803 100644
--- a/src/compiler/crystal/macros/macros.cr
+++ b/src/compiler/crystal/macros/macros.cr
@@ -36,7 +36,7 @@ class Crystal::Program
 
   def parse_macro_source(generated_source, macro_expansion_pragmas, the_macro, node, vars, current_def = nil, inside_type = false, inside_exp = false, visibility : Visibility = :public)
     begin
-      parser = Parser.new(generated_source, @program.string_pool, [vars.dup])
+      parser = @program.new_parser(generated_source, var_scopes: [vars.dup])
       parser.filename = VirtualFile.new(the_macro, generated_source, node.location)
       parser.macro_expansion_pragmas = macro_expansion_pragmas
       parser.visibility = visibility
diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 83cd8f910d63..115b771a399a 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -170,7 +170,7 @@ module Crystal
         arg.raise "argument to parse_type cannot be an empty value" if type_name.blank?
 
         begin
-          parser = Crystal::Parser.new type_name
+          parser = @program.new_parser type_name
           parser.next_token
           type = parser.parse_bare_proc_type
           parser.check :EOF
diff --git a/src/compiler/crystal/program.cr b/src/compiler/crystal/program.cr
index 30c1870e5396..55673ecc38f8 100644
--- a/src/compiler/crystal/program.cr
+++ b/src/compiler/crystal/program.cr
@@ -248,6 +248,12 @@ module Crystal
       define_macro_types
     end
 
+    # Returns a new `Parser` for the given *source*, sharing the string pool and
+    # warnings with this program.
+    def new_parser(source : String, var_scopes = [Set(String).new])
+      Parser.new(source, string_pool, var_scopes, warnings)
+    end
+
     # Returns a `LiteralExpander` useful to expand literal like arrays and hashes
     # into simpler forms.
     getter(literal_expander) { LiteralExpander.new self }
diff --git a/src/compiler/crystal/semantic/semantic_visitor.cr b/src/compiler/crystal/semantic/semantic_visitor.cr
index 5a7c900696ac..88164a36f914 100644
--- a/src/compiler/crystal/semantic/semantic_visitor.cr
+++ b/src/compiler/crystal/semantic/semantic_visitor.cr
@@ -51,7 +51,7 @@ abstract class Crystal::SemanticVisitor < Crystal::Visitor
       nodes = Array(ASTNode).new(filenames.size)
       filenames.each do |filename|
         if @program.requires.add?(filename)
-          parser = Parser.new File.read(filename), @program.string_pool
+          parser = @program.new_parser(File.read(filename))
           parser.filename = filename
           parser.wants_doc = @program.wants_doc?
           parsed_nodes = parser.parse
diff --git a/src/compiler/crystal/syntax/exception.cr b/src/compiler/crystal/syntax/exception.cr
index c906b22c8b1d..3bc3591de017 100644
--- a/src/compiler/crystal/syntax/exception.cr
+++ b/src/compiler/crystal/syntax/exception.cr
@@ -34,7 +34,6 @@ module Crystal
     def append_to_s(io : IO, source)
       msg = @message.to_s
       error_message_lines = msg.lines
-      default_message = "syntax error in #{@filename}:#{@line_number}"
 
       io << error_body(source, default_message)
       io << '\n'
@@ -42,6 +41,12 @@ module Crystal
       io << remaining error_message_lines
     end
 
+    def default_message
+      if (filename = @filename) && (line_number = @line_number)
+        "#{@warning ? "warning" : "syntax error"} in #{filename}:#{line_number}"
+      end
+    end
+
     def to_s_with_source(io : IO, source)
       append_to_s io, source
     end
diff --git a/src/compiler/crystal/syntax/lexer.cr b/src/compiler/crystal/syntax/lexer.cr
index a6cc0f58b495..7f754e6fe5a7 100644
--- a/src/compiler/crystal/syntax/lexer.cr
+++ b/src/compiler/crystal/syntax/lexer.cr
@@ -1,6 +1,7 @@
 require "./token"
 require "../exception"
 require "string_pool"
+require "../warnings"
 
 module Crystal
   class Lexer
@@ -52,7 +53,11 @@ module Crystal
       end
     end
 
-    def initialize(string, string_pool : StringPool? = nil)
+    # Warning settings and all detected warnings.
+    property warnings : WarningCollection
+
+    def initialize(string, string_pool : StringPool? = nil, warnings : WarningCollection? = nil)
+      @warnings = warnings || WarningCollection.new
       @reader = Char::Reader.new(string)
       @token = Token.new
       @temp_token = Token.new
@@ -1473,6 +1478,10 @@ module Crystal
       raise "#{string_range(start, pos_before_suffix)} doesn't fit in an #{type}, try using the suffix #{alternative}", @token, (current_pos - start)
     end
 
+    def warn_large_uint64_literal(start, pos_before_suffix)
+      @warnings.add_warning_at(@token.location, "#{string_range(start, pos_before_suffix)} doesn't fit in an Int64, try using the suffix u64 or i128")
+    end
+
     private def scan_number(start, negative = false)
       @token.type = :NUMBER
       base = 10
@@ -1584,12 +1593,17 @@ module Crystal
                                elsif negative
                                  raise_value_doesnt_fit_in(Int64, start, pos_before_suffix, "i128")
                                else
+                                 warn_large_uint64_literal(start, pos_before_suffix)
                                  NumberKind::U64
                                end
                              when 20
                                raise_value_doesnt_fit_in(Int64, start, pos_before_suffix, "i128") if negative
-                               raise_value_doesnt_fit_in(UInt64, start, pos_before_suffix, "i128") unless raw_number_string.to_u64?
-                               NumberKind::U64
+                               if raw_number_string.to_u64?
+                                 warn_large_uint64_literal(start, pos_before_suffix)
+                                 NumberKind::U64
+                               else
+                                 raise_value_doesnt_fit_in(UInt64, start, pos_before_suffix, "i128")
+                               end
                              when 21..38
                                raise_value_doesnt_fit_in(negative ? Int64 : UInt64, start, pos_before_suffix, "i128")
                              when 39
diff --git a/src/compiler/crystal/syntax/parser.cr b/src/compiler/crystal/syntax/parser.cr
index cb3f6b19ca88..48e45bbf3296 100644
--- a/src/compiler/crystal/syntax/parser.cr
+++ b/src/compiler/crystal/syntax/parser.cr
@@ -24,8 +24,8 @@ module Crystal
       new(str, string_pool, var_scopes).parse
     end
 
-    def initialize(str, string_pool : StringPool? = nil, @var_scopes = [Set(String).new])
-      super(str, string_pool)
+    def initialize(str, string_pool : StringPool? = nil, @var_scopes = [Set(String).new], warnings : WarningCollection? = nil)
+      super(str, string_pool, warnings)
       @unclosed_stack = [] of Unclosed
       @calls_super = false
       @calls_initialize = false
diff --git a/src/compiler/crystal/tools/formatter.cr b/src/compiler/crystal/tools/formatter.cr
index 3c5269a65584..64b6814270c9 100644
--- a/src/compiler/crystal/tools/formatter.cr
+++ b/src/compiler/crystal/tools/formatter.cr
@@ -1,16 +1,22 @@
 require "../syntax"
 
 module Crystal
-  def self.format(source, filename = nil)
-    Crystal::Formatter.format(source, filename: filename)
+  def self.format(source, filename = nil, report_warnings : IO? = nil)
+    Crystal::Formatter.format(source, filename: filename, report_warnings: report_warnings)
   end
 
   class Formatter < Visitor
-    def self.format(source, filename = nil)
+    def self.format(source, filename = nil, report_warnings : IO? = nil)
       parser = Parser.new(source)
       parser.filename = filename
       nodes = parser.parse
 
+      # the formatter merely parses the same source again, it shouldn't
+      # introduce any new syntax warnings the parser cannot find
+      if report_warnings
+        parser.warnings.report(report_warnings)
+      end
+
       formatter = new(source)
       formatter.skip_space_or_newline
       nodes.accept formatter
diff --git a/src/compiler/crystal/tools/playground/server.cr b/src/compiler/crystal/tools/playground/server.cr
index cc535f1609d7..4b8ee5f160a2 100644
--- a/src/compiler/crystal/tools/playground/server.cr
+++ b/src/compiler/crystal/tools/playground/server.cr
@@ -16,6 +16,7 @@ module Crystal::Playground
     end
 
     def self.instrument_and_prelude(session_key, port, tag, source, host : String? = "localhost")
+      # TODO: figure out how syntax warnings should be reported
       ast = Parser.new(source).parse
 
       instrumented = Playground::AgentInstrumentorTransformer.transform(ast).to_s
diff --git a/src/int.cr b/src/int.cr
index e4e9aa452963..7ad4c39daaef 100644
--- a/src/int.cr
+++ b/src/int.cr
@@ -6,8 +6,8 @@
 #
 # An integer literal is an optional `+` or `-` sign, followed by
 # a sequence of digits and underscores, optionally followed by a suffix.
-# If no suffix is present, the literal's type is the lowest between `Int32`, `Int64` and `UInt64`
-# in which the number fits:
+# If no suffix is present, the literal's type is `Int32`, or `Int64` if the
+# number doesn't fit into an `Int32`:
 #
 # ```
 # 1 # Int32
@@ -25,10 +25,14 @@
 # +10 # Int32
 # -20 # Int32
 #
-# 2147483648          # Int64
-# 9223372036854775808 # UInt64
+# 2147483648 # Int64
 # ```
 #
+# Literals without a suffix that are larger than `Int64::MAX` represent a
+# `UInt64` if the number fits, e.g. `9223372036854775808` and
+# `0x80000000_00000000`. This behavior is deprecated and will become an error in
+# the future.
+#
 # The underscore `_` before the suffix is optional.
 #
 # Underscores can be used to make some numbers more readable:
diff --git a/src/string.cr b/src/string.cr
index 1823c0cd9139..a9eba0dc9d1b 100644
--- a/src/string.cr
+++ b/src/string.cr
@@ -459,7 +459,7 @@ class String
 
   # Same as `#to_i` but returns an `Int64` or the block's value.
   def to_i64(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &block)
-    gen_to_ Int64, UInt64, 9223372036854775807, 9223372036854775808
+    gen_to_ Int64, UInt64, 9223372036854775807, 9223372036854775808u64
   end
 
   # Same as `#to_i` but returns an `UInt64`.