diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index f7a908a..4dac822 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -162,10 +162,7 @@ function aggregator_menu() {
   $items['aggregator/categories/%aggregator_category'] = array(
     'title callback' => '_aggregator_category_title',
     'title arguments' => array(2),
-    'page callback' => 'aggregator_page_category',
-    'page arguments' => array(2),
-    'access arguments' => array('access news feeds'),
-    'file' => 'aggregator.pages.inc',
+    'route_name' => 'aggregator_category',
   );
   $items['aggregator/categories/%aggregator_category/view'] = array(
     'title' => 'View',
@@ -242,13 +239,14 @@ function aggregator_menu() {
 /**
  * Title callback: Returns a title for aggregator category pages.
  *
- * @param $category
- *   An aggregator category.
+ * @param int $cid
+ *   An aggregator category id.
  *
- * @return
+ * @return string
  *   A string with the aggregator category title.
  */
-function _aggregator_category_title($category) {
+function _aggregator_category_title($cid) {
+  $category = db_query('SELECT cid, title FROM {aggregator_category} WHERE cid = :cid', array(':cid' => $cid))->fetchObject();
   return $category->title;
 }
 
diff --git a/core/modules/aggregator/aggregator.pages.inc b/core/modules/aggregator/aggregator.pages.inc
index c524505..44436f1 100644
--- a/core/modules/aggregator/aggregator.pages.inc
+++ b/core/modules/aggregator/aggregator.pages.inc
@@ -65,7 +65,7 @@ function aggregator_page_category($category) {
   // database by aggregator_category_load().
   $items = aggregator_load_feed_items('category', $category);
 
-  return _aggregator_page_list($items, arg(3));
+  return _aggregator_page_list($items, $category->cid);
 }
 
 /**
diff --git a/core/modules/aggregator/aggregator.routing.yml b/core/modules/aggregator/aggregator.routing.yml
index 2c69045..735e087 100644
--- a/core/modules/aggregator/aggregator.routing.yml
+++ b/core/modules/aggregator/aggregator.routing.yml
@@ -67,3 +67,10 @@ aggregator_categories:
     _content: '\Drupal\aggregator\Controller\AggregatorController::categories'
   requirements:
     _access_aggregator_categories: 'TRUE'
+
+aggregator_category:
+  pattern: '/aggregator/categories/{cid}'
+  defaults:
+    _controller: '\Drupal\aggregator\Controller\AggregatorController::category'
+  requirements:
+    _permission: 'access news feeds'
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php b/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
index 3fd7dae..d35ed7d 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
@@ -323,4 +323,27 @@ public function sources() {
     return $build;
   }
 
+  /**
+   * Displays feed items aggregated in a category.
+   *
+   * @param int $cid
+   *   The category id for which to list all of the aggregated items.
+   *
+   * @return string
+   *   The rendered list of items for the feed.
+   */
+  public function category($cid) {
+    $category = $this->database->query('SELECT cid, title FROM {aggregator_category} WHERE cid = :cid', array(':cid' => $cid))->fetchObject();
+    drupal_add_feed('aggregator/rss/' . $category->cid, $this->configFactory->get('system.site')->get('name') . ' ' . t('aggregator - @title', array('@title' => $category->title)));
+
+    // @todo move included functions to controller.
+    module_load_include('inc', 'aggregator', 'aggregator.pages');
+
+    // It is safe to include the cid in the query because it's loaded from the
+    // database by aggregator_category_load().
+    $items = aggregator_load_feed_items('category', $category);
+
+    return _aggregator_page_list($items, $cid);
+  }
+
 }