diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index d2c07af..be11fea 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -59,6 +59,7 @@ function aggregator_theme() {
     ),
     'aggregator_block_item' => array(
       'variables' => array('item' => NULL, 'feed' => 0),
+      'template' => 'aggregator-block-item',
     ),
     'aggregator_summary_items' => array(
       'variables' => array('summary_items' => NULL, 'source' => NULL),
@@ -68,6 +69,7 @@ function aggregator_theme() {
     'aggregator_summary_item' => array(
       'variables' => array('aggregator_item' => NULL, 'view_mode' => NULL),
       'file' => 'aggregator.pages.inc',
+      'template' => 'aggregator-summary-item',
     ),
     'aggregator_item' => array(
       'variables' => array('aggregator_item' => NULL, 'view_mode' => NULL),
@@ -488,18 +490,19 @@ function aggregator_category_load($cid) {
 }
 
 /**
- * Returns HTML for an individual feed item for display in the block.
+ * Prepares variables for individual feed item block templates.
  *
- * @param $variables
+ * Default template: aggregator-block-item.html.twig.
+ *
+ * @param array $variables
  *   An associative array containing:
  *   - item: The item to be displayed.
  *   - feed: Not used.
- *
- * @ingroup themeable
  */
-function theme_aggregator_block_item($variables) {
+function template_preprocess_aggregator_block_item(&$variables) {
   // Display the external link to the item.
-  return '<a href="' . check_url($variables['item']->link) . '">' . check_plain($variables['item']->title) . "</a>\n";
+  $variables['url'] = check_url($variables['item']->link);
+  $variables['title'] = check_plain($variables['item']->title);
 }
 
 /**
diff --git a/core/modules/aggregator/aggregator.pages.inc b/core/modules/aggregator/aggregator.pages.inc
index b6d4062..0ac07f1 100644
--- a/core/modules/aggregator/aggregator.pages.inc
+++ b/core/modules/aggregator/aggregator.pages.inc
@@ -7,6 +7,7 @@
 
 use Drupal\aggregator\Plugin\Core\Entity\Feed;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Language\Language;
 
 /**
  * Page callback: Displays all the items captured from the particular feed.
@@ -266,21 +267,6 @@ function aggregator_categorize_items_submit($form, &$form_state) {
 }
 
 /**
- * Default theme implementation to present a linked feed item for summaries.
- *
- * @param $variables
- *   An associative array containing:
- *   - item_link: Link to item.
- *   - item_age: Age of the item.
- *
- * @see template_preprocess()
- * @see template_preprocess_aggregator_summary_item()
- */
-function theme_aggregator_summary_item($variables) {
-  return $variables['item_url'] . ' ' . $variables['item_age'];
-}
-
-/**
  * Prepares variables for aggregator item templates.
  *
  * Default template: aggregator-item.html.twig.
diff --git a/core/modules/aggregator/templates/aggregator-block-item.html.twig b/core/modules/aggregator/templates/aggregator-block-item.html.twig
new file mode 100644
index 0000000..10bc490
--- /dev/null
+++ b/core/modules/aggregator/templates/aggregator-block-item.html.twig
@@ -0,0 +1,16 @@
+{#
+/**
+ * @file
+ * Default theme implementation for feed item for display in the block.
+ *
+ * Available variables:
+ * - url: URL to the feed item.
+ * - title: Title of the feed item.
+ *
+ * @see template_preprocess()
+ * @see template_preprocess_aggregator_block_item()
+ *
+ * @ingroup themeable
+ */
+#}
+<a href="{{ url }}">{{ title }}</a>
diff --git a/core/modules/aggregator/templates/aggregator-summary-item.html.twig b/core/modules/aggregator/templates/aggregator-summary-item.html.twig
new file mode 100644
index 0000000..6e2d8b1
--- /dev/null
+++ b/core/modules/aggregator/templates/aggregator-summary-item.html.twig
@@ -0,0 +1,16 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a single feed in a list of feed items.
+ *
+ * Available variables:
+ * - link: Link to item.
+ * - age: Age of the item.
+ *
+ * @see template_preprocess()
+ * @see template_preprocess_aggregator_summary_item()
+ *
+ * @ingroup themeable
+ */
+#}
+{{ url }} {{ age }}