diff --git a/spec/std/time/format_spec.cr b/spec/std/time/format_spec.cr
index 3a95d50d0eea..08baa2e910fd 100644
--- a/spec/std/time/format_spec.cr
+++ b/spec/std/time/format_spec.cr
@@ -204,6 +204,12 @@ describe Time::Format do
     Time.parse!("2017-12-01 20:15:13 +01:00", "%F %T %:z").to_s("%F %T %:z").should eq "2017-12-01 20:15:13 +01:00"
   end
 
+  it "gives nice error message when end of input is reached (#12047)" do
+    expect_raises(Time::Format::Error, "Expected '-' but the end of the input was reached") do
+      Time.parse!("2021-01", "%F")
+    end
+  end
+
   it "parses" do
     parse_time("2014", "%Y").year.should eq(2014)
     parse_time("19", "%C").year.should eq(1900)
diff --git a/src/time/format/parser.cr b/src/time/format/parser.cr
index e5587d55e753..95bac1a5799d 100644
--- a/src/time/format/parser.cr
+++ b/src/time/format/parser.cr
@@ -502,6 +502,14 @@ struct Time::Format
     end
 
     def char(char, *alternatives)
+      unless @reader.has_next?
+        if alternatives.empty?
+          raise "Expected #{char.inspect} but the end of the input was reached"
+        else
+          raise "Expected one of #{char.inspect}, #{alternatives.join(", ", &.inspect)} but reached the input end"
+        end
+      end
+
       unless char?(char, *alternatives)
         raise "Unexpected char: #{current_char.inspect}"
       end