diff --git a/lib/redmine/syntax_highlighting.rb b/lib/redmine/syntax_highlighting.rb
index e2d47f277..866456bf0 100644
--- a/lib/redmine/syntax_highlighting.rb
+++ b/lib/redmine/syntax_highlighting.rb
@@ -76,6 +76,13 @@ module Redmine
         # Highlights +text+ as the content of +filename+
         # Should not return line numbers nor outer pre tag
         def highlight_by_filename(text, filename)
+          # TODO: Delete the following workaround for #30434 and
+          # test_syntax_highlight_should_normalize_line_endings in
+          # application_helper_test.rb when Rouge is improved to
+          # handle CRLF properly.
+          # See also: https://github.com/jneen/rouge/pull/1078
+          text = text.gsub(/\r\n?/, "\n")
+
           lexer =::Rouge::Lexer.guess_by_filename(filename)
           formatter = ::Rouge::Formatters::HTML.new
           ::Rouge.highlight(text, lexer, CustomHTMLLinewise.new(formatter))
diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 5561e2f40..48304af25 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -1123,6 +1123,10 @@ EXPECTED
     end
   end
 
+  def test_syntax_highlight_should_normalize_line_endings
+    assert_equal "line 1\nline 2\n", syntax_highlight("test.txt", "line 1\rline 2\r\n")
+  end
+
   def test_to_path_param
     assert_equal 'test1/test2', to_path_param('test1/test2')
     assert_equal 'test1/test2', to_path_param('/test1/test2/')