diff --git a/core/lib/Drupal/Core/Render/Renderer.php b/core/lib/Drupal/Core/Render/Renderer.php
index 189c2de..42aed78 100644
--- a/core/lib/Drupal/Core/Render/Renderer.php
+++ b/core/lib/Drupal/Core/Render/Renderer.php
@@ -245,9 +245,8 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
       $elements['#children'] = '';
     }
 
-    // @todo Simplify after https://drupal.org/node/2273925
     if (isset($elements['#markup'])) {
-      $elements['#markup'] = SafeMarkup::set($elements['#markup']);
+      $elements['#markup'] = SafeMarkup::checkAdminXss($elements['#markup']);
     }
 
     // Assume that if #theme is set it represents an implemented hook.
@@ -801,7 +800,7 @@ public function generateCachePlaceholder($callback, array &$context) {
       'token' => Crypt::randomBytesBase64(55),
     ];
 
-    return '<drupal-render-cache-placeholder callback="' . $callback . '" token="' . $context['token'] . '"></drupal-render-cache-placeholder>';
+    return SafeMarkup::set('<drupal-render-cache-placeholder callback="' . $callback . '" token="' . $context['token'] . '"></drupal-render-cache-placeholder>');
   }
 
 }
diff --git a/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
index d10078b..ba02605 100644
--- a/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
+++ b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
@@ -47,7 +47,8 @@ public function getInfo() {
    * @see _contextual_links_to_id()
    */
   public static function preRenderPlaceholder(array $element) {
-    $element['#markup'] = '<div' . new Attribute(array('data-contextual-id' => $element['#id'])) . '></div>';
+    // @todo Consider String::format instead.
+    $element['#markup'] = SafeMarkup::set('<div' . new Attribute(array('data-contextual-id' => $element['#id'])) . '></div>');
     return $element;
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Render/RendererPostRenderCacheTest.php b/core/tests/Drupal/Tests/Core/Render/RendererPostRenderCacheTest.php
index 46a49be..70833ba 100644
--- a/core/tests/Drupal/Tests/Core/Render/RendererPostRenderCacheTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/RendererPostRenderCacheTest.php
@@ -416,7 +416,7 @@ public function testPlaceholder() {
       '#prefix' => '<pre>',
       '#suffix' => '</pre>',
     ];
-    $expected_output = '<pre><bar>' . $context['bar'] . '</bar></pre>';
+    $expected_output = '<pre><code>' . $context['bar'] . '</code></pre>';
 
     // #cache disabled.
     $element = $test_element;
@@ -513,7 +513,7 @@ public function testChildElementPlaceholder() {
         '#suffix' => '</pre>'
       ],
     ];
-    $expected_output = '<pre><bar>' . $context['bar'] . '</bar></pre>' . "\n";
+    $expected_output = '<pre><code>' . $context['bar'] . '</code></pre>' . "\n";
 
     // #cache disabled.
     $element = $test_element;
diff --git a/core/tests/Drupal/Tests/Core/Render/RendererTest.php b/core/tests/Drupal/Tests/Core/Render/RendererTest.php
index 455834e..fb712c6 100644
--- a/core/tests/Drupal/Tests/Core/Render/RendererTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/RendererTest.php
@@ -75,6 +75,10 @@ public function providerTestRenderBasic() {
     $data[] = [[
       'child' => ['#markup' => 'bar'],
     ], 'bar'];
+    // XSS filtering test.
+    $data[] = [[
+      'child' => ['#markup' => 'This is <script>alert(\'XSS\')</script> test'],
+    ], 'This is alert(\'XSS\') test'];
     // #children set but empty, and renderable children.
     $data[] = [[
       '#children' => '',
diff --git a/core/tests/Drupal/Tests/Core/Render/RendererTestBase.php b/core/tests/Drupal/Tests/Core/Render/RendererTestBase.php
index cf08554..6b18bb1 100644
--- a/core/tests/Drupal/Tests/Core/Render/RendererTestBase.php
+++ b/core/tests/Drupal/Tests/Core/Render/RendererTestBase.php
@@ -205,7 +205,7 @@ public static function callback(array $element, array $context) {
   public static function placeholder(array $element, array $context) {
     $placeholder = \Drupal::service('renderer')->generateCachePlaceholder(__NAMESPACE__ . '\\PostRenderCache::placeholder', $context);
     $replace_element = array(
-      '#markup' => '<bar>' . $context['bar'] . '</bar>',
+      '#markup' => '<code>' . $context['bar'] . '</code>',
       '#attached' => array(
         'drupalSettings' => [
           'common_test' => $context,