diff --git a/core/lib/Drupal/Core/Render/Element/RenderElement.php b/core/lib/Drupal/Core/Render/Element/RenderElement.php
index 239916b..5579483 100644
--- a/core/lib/Drupal/Core/Render/Element/RenderElement.php
+++ b/core/lib/Drupal/Core/Render/Element/RenderElement.php
@@ -171,7 +171,7 @@ public static function preRenderAjaxForm($element) {
 
     // If #ajax is TRUE, convert it to an empty array. Depending on the #type,
     // it will still be given an event.
-    if (!is_array($element['#ajax'])) {
+    if ($element['#ajax'] === TRUE) {
       $element['#ajax'] = [];
     }
 
diff --git a/core/modules/views_ui/src/ViewUI.php b/core/modules/views_ui/src/ViewUI.php
index 074e612..2e3400e 100644
--- a/core/modules/views_ui/src/ViewUI.php
+++ b/core/modules/views_ui/src/ViewUI.php
@@ -545,6 +545,8 @@ public function renderPreview($display_id, $args = array()) {
     $executable = $this->getExecutable();
     /** @var \Drupal\Core\Render\RendererInterface $renderer */
     $renderer = \Drupal::service('renderer');
+    /** @var \Drupal\Core\Render\RenderCacheInterface $render_cache */
+    $render_cache = \Drupal::service('render_cache');
 
     // Determine where the query and performance statistics should be output.
     $config = \Drupal::config('views.settings');
@@ -857,8 +859,8 @@ public function renderPreview($display_id, $args = array()) {
       // We render the preview now, in order to render it in the context of the
       // previous setup request, because for example pager links depend on the
       // "current" URL.
-      $renderer->render($output['preview']);
-      $output['preview']['#printed'] = FALSE;
+      $renderer->renderPlain($output['preview']);
+      $output['preview'] = $render_cache->getCacheableRenderArray($output['preview']);
     }
 
     // Ensure that we just remove an additional request we pushed earlier.