diff --git a/Parser/pgenmain.c b/Parser/pgenmain.c
index 4b7b55a..52b8380 100644
--- a/Parser/pgenmain.c
+++ b/Parser/pgenmain.c
@@ -29,6 +29,8 @@
 /* Forward */
 grammar *getgrammar(char *filename);
 
+void Py_Exit(int) _Py_NO_RETURN;
+
 void
 Py_Exit(int sts)
 {