diff --git a/src/aes.js b/src/aes.js
index df7e1b2..aaf6e92 100644
--- a/src/aes.js
+++ b/src/aes.js
@@ -76,15 +76,18 @@
      */
     var AES = C_algo.AES = BlockCipher.extend({
         _doReset: function () {
-            if (this._nRounds) return;
+            // Skip reset of nRounds has been set before and key did not change
+            if (this._nRounds && this._keyPriorReset === this._key) {
+                return;
+            }
 
             // Shortcuts
-            var key = this._key;
+            var key = this._keyPriorReset = this._key;
             var keyWords = key.words;
             var keySize = key.sigBytes / 4;
 
             // Compute number of rounds
-            var nRounds = this._nRounds = keySize + 6
+            var nRounds = this._nRounds = keySize + 6;
 
             // Compute number of key schedule rows
             var ksRows = (nRounds + 1) * 4;