diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 423aae1..39d7327 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -1398,6 +1398,8 @@
 	if (arena == NULL)
 		return NULL;
 
+	flags.cf_flags = 0;
+
 	mod = PyParser_ASTFromString(str, filename, start, &flags, arena);
 	if (mod == NULL) {
 		PyArena_Free(arena);