diff --git a/core/lib/Drupal/Core/Ajax/AjaxResponse.php b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
index 12250b9..3769750 100644
--- a/core/lib/Drupal/Core/Ajax/AjaxResponse.php
+++ b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
@@ -66,12 +66,13 @@ protected function ajaxRender($request) {
     // added during this request to be loaded by the page. We only want to send
     // back files that the page hasn't already loaded, so we implement simple
     // diffing logic using array_diff_key().
+    $ajax_page_state = $request->request->get('ajax_page_state');
     foreach (array('css', 'js') as $type) {
       // It is highly suspicious if $_POST['ajax_page_state'][$type] is empty,
       // since the base page ought to have at least one JS file and one CSS file
       // loaded. It probably indicates an error, and rather than making the page
       // reload all of the files, instead we return no new files.
-      if (empty($request->parameters['ajax_page_state'][$type])) {
+      if (empty($ajax_page_state[$type])) {
         $items[$type] = array();
       }
       else {
@@ -90,7 +91,7 @@ protected function ajaxRender($request) {
           }
         }
         // Ensure that the page doesn't reload what it already has.
-        $items[$type] = array_diff_key($items[$type], $request->parameters['ajax_page_state'][$type]);
+        $items[$type] = array_diff_key($items[$type], $ajax_page_state[$type]);
       }
     }