diff --git a/javascript/07_linkedlist/LinkedListAlgo.js b/javascript/07_linkedlist/LinkedListAlgo.js
index 77695c99..32ee6d14 100644
--- a/javascript/07_linkedlist/LinkedListAlgo.js
+++ b/javascript/07_linkedlist/LinkedListAlgo.js
@@ -169,7 +169,7 @@ class LinkedList {
     findMiddleNode() {
         let fast = this.head
         let slow = this.head
-        while (fast.next !== null && fast.next.next !== null) {
+        while (fast.next !== null && fast.next !== null && fast.next.next !== null) {
             fast = fast.next.next
             slow = slow.next
         }
@@ -247,4 +247,4 @@ let sortedList = mergeSortedLists(sortedList1.head.next, sortedList2.head.next)
 while (sortedList !== null) {
     console.log(sortedList.element)
     sortedList = sortedList.next
-}
\ No newline at end of file
+}