diff --git a/src/underscore.js b/src/underscore.js
index 465071fd2..dc8e55d65 100644
--- a/src/underscore.js
+++ b/src/underscore.js
@@ -37,7 +37,7 @@ function isEqual(val1, val2) {
     if (Array.isArray(val1) && Array.isArray(val2)) {
         if (val1.length !== val2.length) return false;
         return val1.every((item, index) => isEqual(item, val2[index]));
-    } else if (typeof val1 === 'object' && typeof val2 === 'object') {
+    } else if (val1 !== null && typeof val1 === 'object' && val2 !== null && typeof val2 === 'object') {
         const keys1 = Object.keys(val1), keys2 = Object.keys(val2);
         if (keys1.length !== keys2.length) return false;
         return keys1.every(key => isEqual(val1[key], val2[key])); // Recursively compare object properties