diff --git a/lib/XMLHttpRequest.js b/lib/XMLHttpRequest.js
index 4893913..7d6146c 100644
--- a/lib/XMLHttpRequest.js
+++ b/lib/XMLHttpRequest.js
@@ -15,7 +15,7 @@ var Url = require("url");
 var spawn = require("child_process").spawn;
 var fs = require("fs");
 
-exports.XMLHttpRequest = function() {
+exports.XMLHttpRequest = function XMLHttpRequest() {
   "use strict";
 
   /**
@@ -542,7 +542,14 @@ exports.XMLHttpRequest = function() {
       request = null;
     }
 
-    headers = defaultHeaders;
+    headers = {};
+    for (var name in defaultHeaders) {
+      headers[name] = defaultHeaders[name];
+    }    
+    // Remove Accept header so that it can be set via setRequestHeader(),
+    // otherwise, setRequestHeader() would append to it.
+    delete headers["Accept"];
+
     this.status = 0;
     this.responseText = "";
     this.responseXML = "";