diff --git a/lib/stack.c b/lib/stack.c
index 53a9aaa..deba919 100644
--- a/lib/stack.c
+++ b/lib/stack.c
@@ -19,12 +19,14 @@ bool empty(struct stack *stack) {
 }
 
 int length(struct stack *stack) {
+  struct stack *iterator = stack;
   int length = 0;
 
   if (!empty(stack)) {
     length = 1;
-    while (stack->next != NULL) {
+    while (iterator->next != NULL) {
       length++;
+      iterator = iterator->next;
     }
   }