diff --git a/core/modules/aggregator/src/Entity/Feed.php b/core/modules/aggregator/src/Entity/Feed.php
index 1e0a48f..6c964db 100644
--- a/core/modules/aggregator/src/Entity/Feed.php
+++ b/core/modules/aggregator/src/Entity/Feed.php
@@ -117,7 +117,7 @@ public static function postDelete(EntityStorageInterface $storage, array $entiti
       // Make sure there are no active blocks for these feeds.
       $context_ids = [];
       foreach ($entities as $key => $entity) {
-        $context_ids[$key] = 'aggregator.feed:' . $entity->uuid();
+        $context_ids[$key] = '@aggregator.feed_context:' . $entity->uuid();
       }
       $ids = \Drupal::entityQuery('block')
         ->condition('plugin', 'aggregator_feed_block')
diff --git a/core/modules/aggregator/src/Tests/DeleteFeedTest.php b/core/modules/aggregator/src/Tests/DeleteFeedTest.php
index e155584..f40be04 100644
--- a/core/modules/aggregator/src/Tests/DeleteFeedTest.php
+++ b/core/modules/aggregator/src/Tests/DeleteFeedTest.php
@@ -30,10 +30,10 @@ public function testDeleteFeed() {
 
     // Place a block for both feeds.
     $block = $this->drupalPlaceBlock('aggregator_feed_block');
-    $block->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed1->uuid()]);
+    $block->getPlugin()->setContextMapping(['feed' => '@aggregator.feed_context:' . $feed1->uuid()]);
     $block->save();
     $block2 = $this->drupalPlaceBlock('aggregator_feed_block');
-    $block2->getPlugin()->setContextMapping(['feed' => 'aggregator.feed:' . $feed2->uuid()]);
+    $block2->getPlugin()->setContextMapping(['feed' => '@aggregator.feed_context:' . $feed2->uuid()]);
     $block2->save();
 
     // Delete feed.
diff --git a/core/modules/block/tests/src/Unit/BlockRepositoryTest.php b/core/modules/block/tests/src/Unit/BlockRepositoryTest.php
index d837848..5ddeab0 100644
--- a/core/modules/block/tests/src/Unit/BlockRepositoryTest.php
+++ b/core/modules/block/tests/src/Unit/BlockRepositoryTest.php
@@ -40,6 +40,11 @@ class BlockRepositoryTest extends UnitTestCase {
   protected $contextHandler;
 
   /**
+   * @var \Drupal\Core\Plugin\Context\LazyContextRepository|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $contextRepository;
+
+  /**
    * {@inheritdoc}
    */
   protected function setUp() {
@@ -65,13 +70,16 @@ protected function setUp() {
       ->will($this->returnValue($active_theme));
 
     $this->contextHandler = $this->getMock('Drupal\Core\Plugin\Context\ContextHandlerInterface');
+    $this->contextRepository = $this->getMockBuilder('Drupal\Core\Plugin\Context\LazyContextRepository')
+      ->disableOriginalConstructor()
+      ->getMock();
     $this->blockStorage = $this->getMock('Drupal\Core\Entity\EntityStorageInterface');
     $entity_manager = $this->getMock('Drupal\Core\Entity\EntityManagerInterface');
     $entity_manager->expects($this->any())
       ->method('getStorage')
       ->willReturn($this->blockStorage);
 
-    $this->blockRepository = new BlockRepository($entity_manager, $theme_manager, $this->contextHandler);
+    $this->blockRepository = new BlockRepository($entity_manager, $theme_manager, $this->contextHandler, $this->contextRepository);
   }
 
   /**