diff --git a/Python/compile.c b/Python/compile.c
index 90fae6328f4164..ea2fdfdb60405f 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -7116,6 +7116,7 @@ assemble(struct compiler *c, int addNone)
     int j, nblocks;
     PyCodeObject *co = NULL;
     PyObject *consts = NULL;
+    memset(&a, 0, sizeof(struct assembler));
 
     /* Make sure every block that falls off the end returns None.
        XXX NEXT_BLOCK() isn't quite right, because if the last