diff --git a/core/modules/forum/src/Controller/ForumController.php b/core/modules/forum/src/Controller/ForumController.php
index db3c888..6c1a308 100644
--- a/core/modules/forum/src/Controller/ForumController.php
+++ b/core/modules/forum/src/Controller/ForumController.php
@@ -83,6 +83,13 @@ class ForumController extends ControllerBase {
   protected $nodeEntityTypeDefinition;
 
   /**
+   * Comment entity type, we need to get cache tags from here.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeInterface
+   */
+  protected $commentEntityTypeDefinition;
+
+  /**
    * Constructs a ForumController object.
    *
    * @param \Drupal\forum\ForumManagerInterface $forum_manager
@@ -103,8 +110,10 @@ class ForumController extends ControllerBase {
    *   The renderer.
    * @param \Drupal\Core\Entity\EntityTypeInterface $node_entity_type_definition
    *   Node entity type definition object
+   * @param \Drupal\Core\Entity\EntityTypeInterface $comment_entity_type_definition
+   *   Comment entity type definition object
    */
-  public function __construct(ForumManagerInterface $forum_manager, VocabularyStorageInterface $vocabulary_storage, TermStorageInterface $term_storage, AccountInterface $current_user, EntityAccessControlHandlerInterface $node_access, array $field_map, EntityStorageInterface $node_type_storage, RendererInterface $renderer, EntityTypeInterface $node_entity_type_definition) {
+  public function __construct(ForumManagerInterface $forum_manager, VocabularyStorageInterface $vocabulary_storage, TermStorageInterface $term_storage, AccountInterface $current_user, EntityAccessControlHandlerInterface $node_access, array $field_map, EntityStorageInterface $node_type_storage, RendererInterface $renderer, EntityTypeInterface $node_entity_type_definition, EntityTypeInterface $comment_entity_type_definition) {
     $this->forumManager = $forum_manager;
     $this->vocabularyStorage = $vocabulary_storage;
     $this->termStorage = $term_storage;
@@ -114,6 +123,7 @@ public function __construct(ForumManagerInterface $forum_manager, VocabularyStor
     $this->nodeTypeStorage = $node_type_storage;
     $this->renderer = $renderer;
     $this->nodeEntityTypeDefinition = $node_entity_type_definition;
+    $this->commentEntityTypeDefinition = $comment_entity_type_definition;
   }
 
   /**
@@ -132,7 +142,8 @@ public static function create(ContainerInterface $container) {
       $entity_manager->getFieldMap(),
       $entity_manager->getStorage('node_type'),
       $container->get('renderer'),
-      $entity_manager->getDefinition('node')
+      $entity_manager->getDefinition('node'),
+      $entity_manager->getDefinition('comment')
     );
   }
 
@@ -218,11 +229,22 @@ protected function build($forums, TermInterface $term, $topics = array(), $paren
     }
     $this->renderer->addCacheableDependency($build, $config);
 
+    foreach ($forums as $forum) {
+      $this->renderer->addCacheableDependency($build, $forum);
+    }
+    foreach ($topics as $topic) {
+      $this->renderer->addCacheableDependency($build, $topic);
+    }
+    foreach ($parents as $parent) {
+      $this->renderer->addCacheableDependency($build, $parent);
+    }
+    $this->renderer->addCacheableDependency($build, $term);
+
     return [
       'action' => $this->buildActionLinks($config->get('vocabulary'), $term),
       'forum' => $build,
       '#cache' => [
-        'tags' => $this->nodeEntityTypeDefinition->getListCacheTags(),
+        'tags' => Cache::mergeTags($this->nodeEntityTypeDefinition->getListCacheTags(), $this->commentEntityTypeDefinition->getListCacheTags()),
       ],
     ];
   }
diff --git a/core/modules/forum/src/Tests/ForumIndexTest.php b/core/modules/forum/src/Tests/ForumIndexTest.php
index 5ec7a79..c2d6e4e 100644
--- a/core/modules/forum/src/Tests/ForumIndexTest.php
+++ b/core/modules/forum/src/Tests/ForumIndexTest.php
@@ -60,6 +60,7 @@ function testForumIndexStatus() {
     $this->assertText($title, 'Published forum topic appears on index.');
     $this->assertCacheTag('node_list');
     $this->assertCacheTag('config:node.type.forum');
+    $this->assertCacheTag('comment_list');
 
     // Unpublish the node.
     $this->drupalPostForm('node/' . $node->id() . '/edit', array(), t('Save and unpublish'));