diff --git a/core/lib/Drupal/Core/AjaxController.php b/core/lib/Drupal/Core/AjaxController.php
index 31259fb..f3eed0a 100644
--- a/core/lib/Drupal/Core/AjaxController.php
+++ b/core/lib/Drupal/Core/AjaxController.php
@@ -50,6 +50,7 @@ public function content(Request $request, $_content) {
     // Remove the accept header so the subrequest does not end up back in this
     // controller.
     $request->headers->remove('accept');
+    $request->headers->remove('x-requested-with');
 
     $response = $this->container->get('http_kernel')->forward($controller, $attributes->all(), $request->query->all());
     // For successful (HTTP status 200) responses.
diff --git a/core/lib/Drupal/Core/HttpKernel.php b/core/lib/Drupal/Core/HttpKernel.php
index ca0c002..ce3272f 100644
--- a/core/lib/Drupal/Core/HttpKernel.php
+++ b/core/lib/Drupal/Core/HttpKernel.php
@@ -72,7 +72,12 @@ public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQ
      */
     public function forward($controller, array $attributes = array(), array $query = array())
     {
-        $attributes['_controller'] = $controller;
+        if (isset($controller)) {
+          $attributes['_controller'] = $controller;
+        }
+        else {
+          unset($attributes['_controller']);
+        }
         $subRequest = $this->container->get('request')->duplicate($query, null, $attributes);
 
         return $this->handle($subRequest, HttpKernelInterface::SUB_REQUEST);