diff --git a/Python/modsupport.c b/Python/modsupport.c
index 518d433..63f5267 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -305,7 +305,7 @@
 		case 'S':
 		case 'O':
 		if (**p_format == '&') {
-			typedef object *(*converter)(void *);
+			typedef object *(*converter) PROTO((void *));
 			converter func = va_arg(*p_va, converter);
 			void *arg = va_arg(*p_va, void *);
 			++*p_format;