diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php
index c9fe040..79735b0 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php
@@ -65,7 +65,8 @@ public function blockSubmit($form, &$form_state) {
    * {@inheritdoc}
    */
   public function build() {
-    $id = $this->getPluginId();
+    // Plugin IDs look something like this: aggregator_category_block:1.
+    list(, $id) = explode(':', $this->getPluginId());
     if ($category = db_query('SELECT cid, title, block FROM {aggregator_category} WHERE cid = :cid', array(':cid' => $id))->fetchObject()) {
       $result = db_query_range('SELECT i.* FROM {aggregator_category_item} ci LEFT JOIN {aggregator_item} i ON ci.iid = i.iid WHERE ci.cid = :cid ORDER BY i.timestamp DESC, i.iid DESC', 0, $this->configuration['block_count'], array(':cid' => $category->cid));
       $more_link = array(