diff --git a/core/modules/block/src/BlockViewBuilder.php b/core/modules/block/src/BlockViewBuilder.php
index a7cb441..351410a 100644
--- a/core/modules/block/src/BlockViewBuilder.php
+++ b/core/modules/block/src/BlockViewBuilder.php
@@ -219,11 +219,13 @@ public static function preRender($build) {
       // "is the" block, and in particular, #attributes and #contextual_links is
       // information about the *entire* block. Therefore, we must move these
       // properties from $content and merge them into the top-level element.
-      foreach (array('#attributes', '#contextual_links') as $property) {
-        if (isset($content[$property])) {
-          $build[$property] += $content[$property];
-          unset($content[$property]);
-        }
+      if (isset($content['#contextual_links'])) {
+        $build['#contextual_links'] += $content['#contextual_links'];
+        unset($content['#contextual_links']);
+      }
+      if (isset($content['#wrapper_attributes'])) {
+        $build['#attributes'] += $content['#wrapper_attributes'];
+        unset($content['#wrapper_attributes']);
       }
       $build['content'] = $content;
     }