diff --git a/stack/stack.c b/stack/stack.c
index b5ffa0a..6203ae0 100644
--- a/stack/stack.c
+++ b/stack/stack.c
@@ -29,7 +29,7 @@ bool isEmpty(Stack *stack)
 
 bool isFull(Stack *stack)
 {
-    if (stack->topIndex == (int) stack->capacity)
+    if (stack->topIndex == (int) stack->capacity - 1)
         return true;
     else
         return false;