diff -u b/core/modules/aggregator/lib/Drupal/aggregator/Entity/Feed.php b/core/modules/aggregator/lib/Drupal/aggregator/Entity/Feed.php
--- b/core/modules/aggregator/lib/Drupal/aggregator/Entity/Feed.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Entity/Feed.php
@@ -358,7 +358,7 @@
    * @return
    *   An array with the list of duplicated feeds.
    */
-  public function getFeedDuplicates() {
+  public function getDuplicates() {
     $query = \Drupal::entityQuery($this->entityTypeId);
 
     $or_condition = $query->orConditionGroup()
diff -u b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
--- b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
@@ -67,7 +67,7 @@
   public function validate(array $form, array &$form_state) {
     $feed = $this->buildEntity($form, $form_state);
     // Check for duplicate titles.
-    $result = $feed->getFeedDuplicates();
+    $result = $feed->getDuplicates();
     foreach ($result as $item) {
       if (strcasecmp($item->label(), $feed->label()) == 0) {
         $this->setFormError('title', $form_state, $this->t('A feed named %feed already exists. Enter a unique title.', array('%feed' => $feed->label())));
diff -u b/core/modules/aggregator/lib/Drupal/aggregator/FeedInterface.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedInterface.php
--- b/core/modules/aggregator/lib/Drupal/aggregator/FeedInterface.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedInterface.php
@@ -248,5 +248,5 @@
    *   An array with the list of duplicated feeds.
    */
-  public function getFeedDuplicates();
+  public function getDuplicates();
 
 }