diff --git a/compat/src/util.js b/compat/src/util.js
index 8ec376942b..460e492bcf 100644
--- a/compat/src/util.js
+++ b/compat/src/util.js
@@ -17,8 +17,8 @@ export function assign(obj, props) {
  * @returns {boolean}
  */
 export function shallowDiffers(a, b) {
-	for (let i in a) if (i !== '__source' && !(i in b)) return true;
-	for (let i in b) if (i !== '__source' && a[i] !== b[i]) return true;
+	for (let i in a) if (i !== '__source' && a[i] !== b[i]) return true;
+	for (let i in b) if (i !== '__source' && !(i in a)) return true;
 	return false;
 }