diff --git a/stere/browser_spy/xhr_script.py b/stere/browser_spy/xhr_script.py
index 6f063502..2597f5a0 100644
--- a/stere/browser_spy/xhr_script.py
+++ b/stere/browser_spy/xhr_script.py
@@ -6,49 +6,34 @@
 // Number of requests that have been completed.
 document.totalXHRrequests = 0;
 
-// Patch a callback system onto XMLHttpRequest.send()
-// Before a request is sent, a callback is run.
-// Add a callback to the callback queue.
-// If no patch exists yet, it will be created
-function addXHRCallback(callback) {
-    if (XMLHttpRequest.callbacks) {
-        // Already overridden send() so just add the callback
-        XMLHttpRequest.callbacks.push(callback);
-    } else {
-        // Create a callback queue
-        XMLHttpRequest.callbacks = [callback];
-        // Store the native send()
-        var oldSend = XMLHttpRequest.prototype.send;
-        // Override the native send()
-        XMLHttpRequest.prototype.send = function() {
-            // Process the callback queue
-            for (var i = 0; i < XMLHttpRequest.callbacks.length; i++) {
-                XMLHttpRequest.callbacks[i](this);
-            }
-            // Call the native send()
-            oldSend.apply(this, arguments);
-        }
+// Prevent patch from stacking if applied multiple times.
+if (!window.oldSend) {
+    window.oldSend = XMLHttpRequest.prototype.send;
+
+    // Patch a request counter onto XMLHttpRequest.send()
+    XMLHttpRequest.prototype.send = function() {
+        countRequests(this);
+        // Call the native send()
+        window.oldSend.apply(this, arguments);
     }
-}
 
-// Increment a counter every time a request starts,
-//   and adds an event to decrement it when the request is complete.
-addXHRCallback(
-  function(xhr) {
-    document.activeXHRrequests += 1;
-    document.totalXHRrequests += 1;
+    // Increment a counter every time a request starts,
+    //   and add an event to decrement it when the request is complete.
+    var countRequests = function(xhr) {
+        document.activeXHRrequests += 1;
+        document.totalXHRrequests += 1;
 
-    xhr.addEventListener(
-        'loadend', () => {
-            // Decrement counter
-            document.activeXHRrequests -= 1;
+        xhr.addEventListener(
+            'loadend', () => {
+                // Decrement counter
+                document.activeXHRrequests -= 1;
 
-            // For live debugging
-            var remaining_msg = `remaining: ${document.activeXHRrequests}`;
-            var total_msg = `total: ${document.totalXHRrequests}`;
-            console.log('XHR loadend,', remaining_msg, total_msg);
-        }
-    )
-  }
-);
+                // For live debugging
+                var remaining_msg = `remaining: ${document.activeXHRrequests}`;
+                var total_msg = `total: ${document.totalXHRrequests}`;
+                console.log('XHR loadend,', remaining_msg, total_msg);
+            }
+        )
+    }
+}
 """
diff --git a/tests/splinter/test_spy.py b/tests/splinter/test_spy.py
index bd0b4880..0d1e229b 100644
--- a/tests/splinter/test_spy.py
+++ b/tests/splinter/test_spy.py
@@ -89,7 +89,6 @@ def test_xhr_spy_not_added(xhr_test_page):
         xhr_test_page.xhr_spy.wait_for_no_activity()
 
 
-@pytest.mark.xfail
 def test_xhr_spy_multiple_add(xhr_test_page):
     """
     When I add the XHR spy to the page multiple times