diff --git a/dtool/src/cppparser/cppBison.yxx b/dtool/src/cppparser/cppBison.yxx
index 43c0c5603c..42750c11cb 100644
--- a/dtool/src/cppparser/cppBison.yxx
+++ b/dtool/src/cppparser/cppBison.yxx
@@ -1420,6 +1420,11 @@ formal_parameter_identifier:
   $$ = $2;
   $$->add_modifier(IIT_paren);
   $$->add_func_modifier($5, $7);
+}
+        | '(' formal_parameter_identifier ')'
+{
+  $$ = $2;
+  $$->add_modifier(IIT_paren);
 }
         ;