diff -u b/core/modules/media_library/media_library.module b/core/modules/media_library/media_library.module
--- b/core/modules/media_library/media_library.module
+++ b/core/modules/media_library/media_library.module
@@ -178,6 +178,7 @@
       $add_classes($view->displayHandlers->get('default')->options['css_class'], ['js-media-library-view']);
     }
     else {
+      $add_classes($view->display_handler->options['defaults']['css_class'], ['js-media-library-view']);
       $add_classes($view->display_handler->options['css_class'], ['js-media-library-view']);
     }
   }
reverted:
--- b/core/themes/seven/seven.theme
+++ a/core/themes/seven/seven.theme
@@ -347,7 +347,7 @@
   };
 
   if ($view->id() === 'media_library') {
+    if ($view->display_handler->options['defaults']['css_class']) {
-    if (isset($view->display_handler->options['defaults']['css_class'])) {
       $add_classes($view->displayHandlers->get('default')->options['css_class'], ['media-library-view']);
     }
     else {
only in patch2:
unchanged:
--- a/core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php
+++ b/core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php
@@ -10,6 +10,7 @@
 use Drupal\Tests\BrowserTestBase;
 use Drupal\Tests\media\Traits\MediaTypeCreationTrait;
 use Drupal\media\Entity\MediaType;
+use Drupal\views\Views;
 
 /**
  * Tests that the Media Library automatically configures form/view modes.
@@ -26,7 +27,9 @@ class MediaLibraryDisplayModeTest extends BrowserTestBase {
   protected static $modules = [
     'field_ui',
     'media',
+    'media_library',
     'system',
+    'views_ui',
   ];
 
   /**
@@ -46,6 +49,7 @@ protected function setUp(): void {
       'administer media form display',
       'administer media display',
       'administer media types',
+      'administer views',
       'view media',
     ]));
   }
@@ -211,6 +215,27 @@ public function testDisplayModes() {
     $this->assertViewDisplay($type_nine_id, 'media_library');
   }
 
+  /**
+   * Tests for exceptions and successful execution of hook_views_pre_render().
+   */
+  public function testThemedViewPage() {
+    // Configure to always show the default display.
+    $edit = [
+      'ui_show_default_display' => TRUE,
+    ];
+    $this->drupalGet('admin/structure/views/settings');
+    $this->submitForm($edit, 'Save configuration');
+
+    /** @var \Drupal\Core\Render\RendererInterface $renderer */
+    $renderer = \Drupal::service('renderer');
+
+    $view = Views::getView('media_library');
+    $build = $view->buildRenderable();
+    unset($build['#view']->display_handler->options['defaults']);
+    // If this fails then there is a bug.
+    $renderer->renderRoot($build);
+  }
+
   /**
    * Asserts the media library form display components for a media type.
    *