diff --git a/fetch.js b/fetch.js
index 62066877c249ad1f02bf731c7343dcd6cb3d5c9e..3fc58a1b35c172c7d01e8a2ef2095e56baafec0c 100644
--- a/fetch.js
+++ b/fetch.js
@@ -240,6 +240,9 @@
 
     return new Promise(function(resolve, reject) {
       var xhr = new XMLHttpRequest()
+      if (self.credentials === 'cors') {
+        xhr.withCredentials = true;
+      }
 
       function responseURL() {
         if ('responseURL' in xhr) {