diff --git a/slides/cours_11.md b/slides/cours_11.md
index 63be99a02861c4f63cffedc3ed2dbb79dfd92213..3d73d9234bb87c8839bc5594d53b44a2253e8cbb 100644
--- a/slides/cours_11.md
+++ b/slides/cours_11.md
@@ -247,8 +247,8 @@ void stack_pop(stack *s, int *val) {
 
 ```C
 void stack_destroy(stack *s) {
-    while (!stack_is_empty(*s)) {
-        int val = stack_pop(s);
+    while (*s != NULL) {
+        stack_pop(s);
     }
 }
 ```