--- a/Mac/Modules/cf/_CFmodule.c
+++ b/Mac/Modules/cf/_CFmodule.c
@@ -1818,7 +1818,7 @@
 	if (PyString_Check(v)) {
 	    char *cStr;
 	    if (!PyArg_Parse(v, "es", "ascii", &cStr))
-	    	return NULL;
+	    	return 0;
 		*p_itself = CFStringCreateWithCString((CFAllocatorRef)NULL, cStr, kCFStringEncodingASCII);
 		return 1;
 	}