diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index 039c305..2d95302 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -712,8 +712,7 @@ function template_preprocess_forum_icon(&$variables) {
     $variables['icon_title'] = t('Sticky topic');
   }
 
-  $variables['attributes']['class'][] = 'icon';
-  $variables['attributes']['class'][] = 'topic-status-' . $icon_status_class;
+  $variables['icon_status_class'] = $icon_status_class;
   $variables['attributes']['title'] = $variables['icon_title'];
 }
 
diff --git a/core/modules/forum/templates/forum-icon.html.twig b/core/modules/forum/templates/forum-icon.html.twig
index f3447f8..8754fa6 100644
--- a/core/modules/forum/templates/forum-icon.html.twig
+++ b/core/modules/forum/templates/forum-icon.html.twig
@@ -17,7 +17,13 @@
  * @ingroup themeable
  */
 #}
-<div{{ attributes }}>
+{%
+  set classes = [
+    'icon',
+    'topic-status-' ~ icon_status_class|clean_class
+  ]
+%}
+<div{{ attributes.addClass(classes) }}>
   {% if first_new -%}
     <a id="new"></a>
   {%- endif %}