diff --git a/lib/adapters/xhr.js b/lib/adapters/xhr.js
index 0105f52..eb7fe18 100644
--- a/lib/adapters/xhr.js
+++ b/lib/adapters/xhr.js
@@ -5,7 +5,7 @@ var buildURL = require('./../helpers/buildURL');
 var parseHeaders = require('./../helpers/parseHeaders');
 var transformData = require('./../helpers/transformData');
 var isURLSameOrigin = require('./../helpers/isURLSameOrigin');
-var btoa = window.btoa || require('./../helpers/btoa');
+var btoa = window && window.btoa || require('./../helpers/btoa');
 
 module.exports = function xhrAdapter(resolve, reject, config) {
   var requestData = config.data;