diff --git a/core/modules/help_topics/help_topics.module b/core/modules/help_topics/help_topics.module
index 76e89425b7..7b860b5ea8 100644
--- a/core/modules/help_topics/help_topics.module
+++ b/core/modules/help_topics/help_topics.module
@@ -7,7 +7,6 @@
 
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Url;
-use Drupal\help_topics\Plugin\HelpTopic\HelpTopicTwig;
 
 /**
  * Implements hook_help().
diff --git a/core/modules/help_topics/src/Controller/HelpTopicPluginController.php b/core/modules/help_topics/src/Controller/HelpTopicPluginController.php
index 5cdd79473c..37eb58a919 100644
--- a/core/modules/help_topics/src/Controller/HelpTopicPluginController.php
+++ b/core/modules/help_topics/src/Controller/HelpTopicPluginController.php
@@ -7,7 +7,7 @@
 use Drupal\help_topics\Plugin\HelpTopic\HelpTopicPluginManagerInterface;
 use Drupal\Core\Render\RendererInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
-use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
 /**
  * Controller for help topic plugins.
@@ -65,7 +65,7 @@ public function viewHelpTopic($id) {
     $build = [];
 
     if (!$this->helpTopicPluginManager->hasDefinition($id)) {
-      throw new AccessDeniedHttpException();
+      throw new NotFoundHttpException();
     }
     /* @var \Drupal\help_topics\Plugin\HelpTopic\HelpTopicPluginInterface $help_topic */
     $help_topic = $this->helpTopicPluginManager->createInstance($id);
diff --git a/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicPluginManager.php b/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicPluginManager.php
index e7b06b0b0f..fa2ed0d642 100644
--- a/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicPluginManager.php
+++ b/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicPluginManager.php
@@ -8,7 +8,6 @@
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Plugin\DefaultPluginManager;
 use Drupal\Core\Plugin\Factory\ContainerFactory;
-use Drupal\Component\Utility\Html;
 
 /**
  * Provides the default help_topic manager.
@@ -235,7 +234,7 @@ public function getThemeImplementations() {
       $return[$hook] = [
         'variables' => [],
         'path' => drupal_get_path('module', $definition['provider']) . '/help_topics/templates',
-        'template' => Html::cleanCssIdentifier($hook),
+        'template' => $hook,
       ];
     }
     return $return;
diff --git a/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicTwig.php b/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicTwig.php
index 49efd558b7..84a217076e 100644
--- a/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicTwig.php
+++ b/core/modules/help_topics/src/Plugin/HelpTopic/HelpTopicTwig.php
@@ -5,6 +5,7 @@
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Component\Utility\Html;
 
 /**
  * Represents a help topic plugin whose definition comes from a YAML file.
@@ -80,7 +81,7 @@ public function getBody() {
    *   Theme hook.
    */
   public static function getThemeHook($plugin_id) {
-    return 'help_topic_' . $plugin_id;
+    return Html::cleanCssIdentifier('help_topic_' . $plugin_id);
   }
 
 }