diff --git a/spec/compiler/lexer/lexer_spec.cr b/spec/compiler/lexer/lexer_spec.cr
index aa9eaf3e06c8..8575f6e1c14b 100644
--- a/spec/compiler/lexer/lexer_spec.cr
+++ b/spec/compiler/lexer/lexer_spec.cr
@@ -362,6 +362,9 @@ describe "Lexer" do
   assert_syntax_error "0o200_i8", "0o200 doesn't fit in an Int8"
   assert_syntax_error "0b10000000_i8", "0b10000000 doesn't fit in an Int8"
 
+  assert_syntax_error "0b11_f32", "binary float literal is not supported"
+  assert_syntax_error "0o73_f64", "octal float literal is not supported"
+
   # 2**31 - 1
   it_lexes_i32 [["0x7fffffff", "2147483647"], ["0o17777777777", "2147483647"], ["0b1111111111111111111111111111111", "2147483647"]]
   it_lexes_i32 [["0x7fffffff_i32", "2147483647"], ["0o17777777777_i32", "2147483647"], ["0b1111111111111111111111111111111_i32", "2147483647"]]
diff --git a/src/compiler/crystal/syntax/lexer.cr b/src/compiler/crystal/syntax/lexer.cr
index c8f65187a448..333fdadaa452 100644
--- a/src/compiler/crystal/syntax/lexer.cr
+++ b/src/compiler/crystal/syntax/lexer.cr
@@ -1284,6 +1284,13 @@ module Crystal
           raise("unexpected '_' in number", @token, (current_pos - start)) if peek_next_char == '_'
           break unless peek_next_char.in?('0'..'9')
         when 'i', 'u', 'f'
+          if current_char == 'f' && base != 10
+            case base
+            when 2 then raise("binary float literal is not supported", @token, (current_pos - start))
+            when 8 then raise("octal float literal is not supported", @token, (current_pos - start))
+            end
+            break
+          end
           before_suffix_pos = current_pos
           @token.number_kind = consume_number_suffix
           next_char