diff --git a/lib/sinon/util/fake_xml_http_request.js b/lib/sinon/util/fake_xml_http_request.js
index c476aff38..ff4905178 100644
--- a/lib/sinon/util/fake_xml_http_request.js
+++ b/lib/sinon/util/fake_xml_http_request.js
@@ -654,13 +654,16 @@ extend(FakeXMLHttpRequest.prototype, sinonEvent.EventTarget, {
     }
 });
 
-extend(FakeXMLHttpRequest, {
+var states = {
     UNSENT: 0,
     OPENED: 1,
     HEADERS_RECEIVED: 2,
     LOADING: 3,
     DONE: 4
-});
+};
+
+extend(FakeXMLHttpRequest, states);
+extend(FakeXMLHttpRequest.prototype, states);
 
 function useFakeXMLHttpRequest() {
     FakeXMLHttpRequest.restore = function restore(keepOnCreate) {
diff --git a/test/util/fake-xml-http-request-test.js b/test/util/fake-xml-http-request-test.js
index da378556f..f0d130fd8 100644
--- a/test/util/fake-xml-http-request-test.js
+++ b/test/util/fake-xml-http-request-test.js
@@ -132,13 +132,22 @@ if (typeof window !== "undefined") {
             assert.same(FakeXMLHttpRequest.prototype.constructor, FakeXMLHttpRequest);
         });
 
-        it("implements readyState constants", function () {
+        it("class implements readyState constants", function () {
             assert.same(FakeXMLHttpRequest.OPENED, 1);
             assert.same(FakeXMLHttpRequest.HEADERS_RECEIVED, 2);
             assert.same(FakeXMLHttpRequest.LOADING, 3);
             assert.same(FakeXMLHttpRequest.DONE, 4);
         });
 
+        it("instance implements readyState constants", function () {
+            var xhr = new FakeXMLHttpRequest();
+
+            assert.same(xhr.OPENED, 1);
+            assert.same(xhr.HEADERS_RECEIVED, 2);
+            assert.same(xhr.LOADING, 3);
+            assert.same(xhr.DONE, 4);
+        });
+
         it("calls onCreate if listener is set", function () {
             var onCreate = sinonSpy();
             FakeXMLHttpRequest.onCreate = onCreate;