diff --git a/lib/util.js b/lib/util.js
index 22a14c89..68f8674a 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -133,7 +133,12 @@ function base64ToBytes(base64) {
  * @return {string}
  */
 function bytesToBase64(bytes) {
-  return btoa(String.fromCharCode.apply(null, new Uint8Array(bytes)));
+  const uint8Array = new Uint8Array(bytes);
+  let binaryString = "";
+  for (let i = 0; i < uint8Array.length; i++) {
+    binaryString += String.fromCharCode(uint8Array[i]);
+  }
+  return btoa(binaryString);
 }
 
 /**