diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index 681e75c..75c9955 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -610,9 +610,7 @@ protected function registerStreamWrapper($scheme, $class, $type = StreamWrapperI
   protected function render(array &$elements) {
     // Use the bare HTML page renderer to render our links.
     $renderer = $this->container->get('bare_html_page_renderer');
-    $response = $renderer->renderBarePage(
-      $elements, '', $this->container->get('theme.manager')->getActiveTheme()->getName()
-    );
+    $response = $renderer->renderBarePage($elements, '', 'maintenance_page');
 
     // Glean the content from the response object.
     $content = $response->getContent();
diff --git a/core/modules/system/src/Tests/Common/AddFeedTest.php b/core/modules/system/src/Tests/Common/AddFeedTest.php
index 0620051..2e8b4ce 100644
--- a/core/modules/system/src/Tests/Common/AddFeedTest.php
+++ b/core/modules/system/src/Tests/Common/AddFeedTest.php
@@ -63,9 +63,7 @@ function testBasicFeedAddNoTitle() {
 
     // Use the bare HTML page renderer to render our links.
     $renderer = $this->container->get('bare_html_page_renderer');
-    $response = $renderer->renderBarePage(
-      $build, '', $this->container->get('theme.manager')->getActiveTheme()->getName()
-    );
+    $response = $renderer->renderBarePage($build, '', 'maintenance_page');
     // Glean the content from the response object.
     $this->setRawContent($response->getContent());
     // Assert that the content contains the RSS links we specified.
diff --git a/core/modules/system/src/Tests/Common/RenderTest.php b/core/modules/system/src/Tests/Common/RenderTest.php
index 61f7105..03676e7 100644
--- a/core/modules/system/src/Tests/Common/RenderTest.php
+++ b/core/modules/system/src/Tests/Common/RenderTest.php
@@ -57,7 +57,7 @@ public function testProcessAttached() {
     $build['#attached']['drupal_process_states'][] = [];
     $renderer = $this->container->get('bare_html_page_renderer');
     try {
-      $renderer->renderBarePage($build, '', $this->container->get('theme.manager')->getActiveTheme()->getName());
+      $renderer->renderBarePage($build, '', 'maintenance_page');
       $this->fail("Invalid #attachment 'drupal_process_states' allowed");
     }
     catch (\LogicException $e) {
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 0902438..b2646b4 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -945,9 +945,7 @@ protected function render(array &$elements) {
 
     // Use the bare HTML page renderer to render our links.
     $renderer = $this->container->get('bare_html_page_renderer');
-    $response = $renderer->renderBarePage(
-      $elements, '', $this->container->get('theme.manager')->getActiveTheme()->getName()
-    );
+    $response = $renderer->renderBarePage($elements, '', 'maintenance_page');
 
     // Glean the content from the response object.
     $content = $response->getContent();