diff --git a/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml b/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml
index 34f7844..e8d06c0 100644
--- a/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml
+++ b/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml
@@ -35,6 +35,13 @@ ajax_test.render:
   requirements:
     _access: 'TRUE'
 
+ajax_test.admin.theme:
+  path: '/admin/ajax-test/theme'
+  defaults:
+    _controller: '\Drupal\ajax_test\Controller\AjaxTestController::theme'
+  requirements:
+    _access: 'TRUE'
+
 ajax_test.order:
   path: '/ajax-test/order'
   defaults:
diff --git a/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php b/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
index fbbb2b5..9f10db4 100644
--- a/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
+++ b/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
@@ -6,6 +6,7 @@
 use Drupal\Core\Ajax\AlertCommand;
 use Drupal\Core\Ajax\CloseDialogCommand;
 use Drupal\Core\Ajax\HtmlCommand;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -62,6 +63,15 @@ public function render() {
   }
 
   /**
+   * Returns the used theme.
+   */
+  public function theme() {
+    return [
+      '#markup' => 'Current theme: ' . \Drupal::theme()->getActiveTheme()->getName(),
+    ];
+  }
+
+  /**
    * Returns an AjaxResponse; settings command set last.
    *
    * Helps verifying AjaxResponse reorders commands to ensure correct execution.
@@ -184,6 +194,17 @@ public function dialog() {
             ))
           ),
         ),
+        'link8' => [
+          'title' => 'Link 8 (ajax)',
+          'url' => Url::fromRoute('ajax_test.admin.theme'),
+          'attributes' => [
+            'class' => ['use-ajax'],
+            'data-dialog-type' => 'modal',
+            'data-dialog-options' => json_encode([
+              'width' => 400,
+            ])
+          ],
+        ]
       ),
     );
 
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/AjaxThemeTest.php b/core/tests/Drupal/FunctionalJavascriptTests/AjaxThemeTest.php
new file mode 100644
index 0000000..0eb6d19
--- /dev/null
+++ b/core/tests/Drupal/FunctionalJavascriptTests/AjaxThemeTest.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\FunctionalJavascriptTests;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Ensures that ajax themes are rendered in the frontend theme.
+ */
+class AjaxThemeTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['ajax_test'];
+
+  public function testAjaxWithAdminRoute() {
+    \Drupal::service('theme_installer')->install(['seven']);
+    $theme_config = \Drupal::configFactory()->getEditable('system.theme');
+    $theme_config->set('admin', 'seven');
+    $theme_config->save();
+
+    $account = $this->drupalCreateUser(['view the administration theme']);
+    $this->drupalLogin($account);
+
+    // First visit the site directly via the URL. This should render it in the
+    // admin theme.
+    $this->drupalGet('/admin/ajax-test/theme');
+    $assert = $this->assertSession();
+    $assert->pageTextContains('Current theme: seven');
+
+    // Now
+    $this->drupalGet('/ajax-test/dialog');
+    $assert->pageTextNotContains('Current theme: stable');
+    $this->clickLink('Link 8 (ajax)');
+
+    $assert->pageTextContains('Current theme: stable');
+    $assert->pageTextNotContains('Current theme: seven');
+    $this->clickLink('Link 8 (ajax)');
+  }
+  
+
+}