diff -u b/core/modules/menu/menu.module b/core/modules/menu/menu.module
--- b/core/modules/menu/menu.module
+++ b/core/modules/menu/menu.module
@@ -12,7 +12,7 @@
  */
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\block\BlockInterface;
+use Drupal\block\BlockPluginInterface;
 use Drupal\system\Plugin\Core\Entity\Menu;
 use Drupal\system\Plugin\block\block\SystemMenuBlock;
 use Symfony\Component\HttpFoundation\JsonResponse;
@@ -401,7 +401,7 @@
 /**
  * Implements hook_block_view_BASE_BLOCK_ID_alter() for 'system_menu_block'.
  */
-function menu_block_view_system_menu_block_alter(array &$build, BlockInterface $block) {
+function menu_block_view_system_menu_block_alter(array &$build, BlockPluginInterface $block) {
   // Add contextual links for system menu blocks.
   if (isset($build['content'])) {
     foreach (element_children($build['content']) as $key) {