1 files changed, 1 insertions, 1 deletions
diff --git a/eval.c b/eval.c
index df9570e3..cd5a5844 100644
--- a/eval.c
+++ b/eval.c
@@ -1418,7 +1418,7 @@ unwind_stack(long n)
 	if (stack_ptr < sp)
 		return NULL;
 
-	while (r = POP()) {
+	while ((r = POP()) != NULL) {
 		switch (r->type) {
 		case Node_frame:
 			cp = restore_frame(r);