diff --git a/lib/cmock_generator.rb b/lib/cmock_generator.rb
index 1e710555..dfbe3e26 100644
--- a/lib/cmock_generator.rb
+++ b/lib/cmock_generator.rb
@@ -208,7 +208,7 @@ def create_mock_header_footer(header)
   end
 
   def create_source_header_section(file, filename, mock_project)
-    header_file = (mock_project[:folder] || '') + filename.gsub('.c', mock_project[:module_ext])
+    header_file = (mock_project[:folder] || '') + filename.sub(/.*\K\.c/, mock_project[:module_ext])
     file << "/* AUTOGENERATED FILE. DO NOT EDIT. */\n" unless mock_project[:parsed_stuff][:functions].empty?
     file << "#include <string.h>\n"
     file << "#include <stdlib.h>\n"