diff --git a/oauth3.issuer.mock.js b/oauth3.issuer.mock.js
index b618ba0..2afe1ee 100644
--- a/oauth3.issuer.mock.js
+++ b/oauth3.issuer.mock.js
@@ -5,7 +5,7 @@
 
   OAUTH3._base64.btoa = function (b64) {
     // http://stackoverflow.com/questions/9677985/uncaught-typeerror-illegal-invocation-in-chrome
-    (exports.btoa || require('btoa'))(b64);
+    return (exports.btoa || require('btoa'))(b64);
   }
   OAUTH3._base64.encodeUrlSafe = function (b64) {
     // Base64 to URL-safe Base64