diff --git a/backbone.nativeajax.js b/backbone.nativeajax.js
index 3f033b7..9a724c8 100644
--- a/backbone.nativeajax.js
+++ b/backbone.nativeajax.js
@@ -7,10 +7,14 @@
 //     https://github.com/akre54/Backbone.NativeAjax
 
 (function (factory) {
-  if (typeof define === 'function' && define.amd) { define(factory);
-  } else if (typeof exports === 'object') { module.exports = factory();
-  } else { Backbone.ajax = factory(); }
-}(function() {
+  if (typeof define === 'function' && define.amd) { 
+    define(factory.bind(this, this.XMLHttpRequest));
+  } else if (typeof exports === 'object') {
+    module.exports = factory(require('xmlhttprequest').XMLHttpRequest);
+  } else {
+    Backbone.ajax = factory(XMLHttpRequest);
+  }
+}(function(XMLHttpRequest) {
   // Make an AJAX request to the server.
   // Usage:
   //   var req = Backbone.ajax({url: 'url', type: 'PATCH', data: 'data'});
@@ -33,7 +37,7 @@
     var isValid = function(xhr) {
       return (xhr.status >= 200 && xhr.status < 300) ||
         (xhr.status === 304) ||
-        (xhr.status === 0 && window.location.protocol === 'file:')
+        (xhr.status === 0 && typeof window !== "undefined" && window.location.protocol === 'file:')
     };
 
     var end = function(xhr, options, promise, resolve, reject) {
@@ -98,7 +102,11 @@
             '=' + encodeURIComponent(value);
         };
         for (var key in options.data) {
-          query += stringifyKeyValuePair(key, options.data[key]);
+          var value = options.data[key];
+          var values = Array.isArray(value) ? value : [value];
+          for (var i=0; i < values.length; i++) {
+            query += stringifyKeyValuePair(key, values[i]);
+          }
         }
 
         if (query) {
diff --git a/package.json b/package.json
index 711d42b..81bd82d 100644
--- a/package.json
+++ b/package.json
@@ -23,7 +23,7 @@
   "devDependencies": {
     "backbone": "1.2.1",
     "chai": "^3.0.0",
-    "karma": "^0.12.36",
+    "karma": "^0.13.9",
     "karma-chrome-launcher": "^0.1.12",
     "karma-cli": "0.0.4",
     "karma-firefox-launcher": "^0.1.6",
diff --git a/test/ajax.js b/test/ajax.js
index 8260f34..b9cb63f 100644
--- a/test/ajax.js
+++ b/test/ajax.js
@@ -41,6 +41,12 @@ describe('Backbone.NativeAjax', function() {
       expect(open).to.have.been.calledOnce;
       expect(open).to.have.been.calledWithExactly('GET', 'test?a=1&b=2', true);
     });
+    it('should handle multiple values for a GET parameter', function() {
+      ajax({url: 'test', dataType: 'json', data: {a: [1, 2]}});
+
+      expect(open).to.have.been.calledOnce;
+      expect(open).to.have.been.calledWithExactly('GET', 'test?a=1&a=2', true);
+    })
   });
 
   describe('headers', function() {