diff --git a/core/modules/aggregator/aggregator.theme.inc b/core/modules/aggregator/aggregator.theme.inc
index 605025c..27a678b 100644
--- a/core/modules/aggregator/aggregator.theme.inc
+++ b/core/modules/aggregator/aggregator.theme.inc
@@ -38,8 +38,6 @@ function template_preprocess_aggregator_item(&$variables) {
   else {
     $variables['source_date'] = format_date($item->getPostedTime(), 'medium');
   }
-
-  $variables['attributes']['class'][] = 'feed-item';
 }
 
 /**
@@ -170,8 +168,6 @@ function template_preprocess_aggregator_feed_source(&$variables) {
   if (\Drupal::currentUser()->hasPermission('administer news feeds')) {
     $variables['last_checked'] = l($variables['last_checked'], 'admin/config/services/aggregator');
   }
-
-  $variables['attributes']['class'][] = 'feed-source';
 }
 
 /**
diff --git a/core/modules/aggregator/templates/aggregator-feed-source.html.twig b/core/modules/aggregator/templates/aggregator-feed-source.html.twig
index d492904..be26a0f 100644
--- a/core/modules/aggregator/templates/aggregator-feed-source.html.twig
+++ b/core/modules/aggregator/templates/aggregator-feed-source.html.twig
@@ -19,7 +19,7 @@
  * @ingroup themeable
  */
 #}
-<div{{ attributes }}>
+<div{{ attributes.addClass('feed-source') }}>
   {{ source_icon }}
   {{ source_image }}
   <p class="feed-description">{{ source_description }}</p>
diff --git a/core/modules/aggregator/templates/aggregator-item.html.twig b/core/modules/aggregator/templates/aggregator-item.html.twig
index 8c23106..ea35ce8 100644
--- a/core/modules/aggregator/templates/aggregator-item.html.twig
+++ b/core/modules/aggregator/templates/aggregator-item.html.twig
@@ -16,7 +16,7 @@
  * @ingroup themeable
  */
 #}
-<div{{ attributes }}>
+<div{{ attributes.addClass('feed-item') }}>
   <h3 class="feed-item-title">
     <a href="{{ feed_url }}">{{ feed_title }}</a>
   </h3>