diff --git a/cv4/list_ops.c b/cv4/list_ops.c
index 612efd3..9f58a2b 100644
--- a/cv4/list_ops.c
+++ b/cv4/list_ops.c
@@ -6,21 +6,22 @@
 
 list_t *new_list(size_t length, list_element_t elements[]) {
     list_t *list = malloc(sizeof(list_t) + length * sizeof(list_element_t));
-    list->length = length;
     if (!list) {
         return NULL; 
     }
+    list->length = length;
     for (size_t i = 0; i < length; i++) {
         list->elements[i] = elements[i];
     }
     return list;
 }
 
-list_t *append_list(list_t *list1, list_t *list2)
-{
-    size_t length = (list1->length + list2->length);
-    list_t *list3 = new_list(list1->length + list2->length,list1->elements);
-    list3->length = length;
+list_t *append_list(list_t *list1, list_t *list2) {
+    list_t *list3 = new_list(list1->length + list2->length, list1->elements);
+    if (!list3) {
+        return NULL;
+    }
+
     for (size_t i = list1->length; i < list3->length; i++)
         list3->elements[i] = list2->elements[i - list1->length];
     return list3;
@@ -43,7 +44,6 @@ list_t *filter_list(list_t *list, bool (*predicate)(list_element_t)) {
    return result;
 }
 
-
 size_t length_list(list_t *list) {
     return list->length;
 }