diff --git a/lib/fetch.browser.js b/lib/fetch.browser.js
index 75fe9c9..543943f 100644
--- a/lib/fetch.browser.js
+++ b/lib/fetch.browser.js
@@ -152,7 +152,7 @@ function verifyAndExtendResponse(url, options, response) {
   var cachedHeaders;
   function getCachedHeaders() {
     if (!cachedHeaders) {
-      cachedHeaders = {};
+      cachedHeaders = Object.create(originalHeaders);
       originalHeaders.forEach(function addHeader(value, name) {
         if (name) {
           cachedHeaders[name] = value;