diff --git a/slides/cours_9.md b/slides/cours_9.md
index 4e83cd78e6d764c0b4119bd2b83f67b0b9fe4721..8f5474e77ef873d309b5aaec7ba896c2b7db0ae7 100644
--- a/slides/cours_9.md
+++ b/slides/cours_9.md
@@ -535,7 +535,7 @@ typedef element* stack;
 . . .
 
 ```C
-stack stack_create(); // return NULL;
+void stack_create(stack *s); // *s = NULL;
 void stack_destroy(stack *s);
 void stack_push(stack *s, int val);
 void stack_pop(stack *s, int *val);