diff --git a/linked-list.c b/linked-list.c
index a6e18e2..68f968a 100644
--- a/linked-list.c
+++ b/linked-list.c
@@ -50,6 +50,8 @@ void list_print(list_t * list) {
 void list_add(list_t * list, list_node_t * item) {
   list_node_t *cur;
 
+  assert(item->next == NULL);
+
   if (list_empty(list)) {
     list->head = item;
   } else {
@@ -143,6 +145,7 @@ int main(int argc, char *argv[]) {
   for (int i = 0; i < howmany; i++) {
     list_node_t *newnode = malloc(sizeof(list_node_t));
     newnode->data = i;
+    newnode->next = NULL;
 
     list_add(foolist, newnode);
   }
@@ -200,6 +203,7 @@ int main(int argc, char *argv[]) {
   for (int i = 0; i < howmany2; i++) {
     list_node_t *newnode = malloc(sizeof(list_node_t));
     newnode->data = i;
+    newnode->next = NULL;
 
     list_add(foolist, newnode);
   }