diff --git a/Python/cgensupport.c b/Python/cgensupport.c
index b24c80a..a3023eb 100644
--- a/Python/cgensupport.c
+++ b/Python/cgensupport.c
@@ -171,7 +171,7 @@
 {
 	object *v;
 	if (!getiobjectarg(args, nargs, i, &v))
-		return NULL;
+		return 0;
 	if (!is_stringobject(v)) {
 		return err_badarg();
 	}