diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index 0fce7ec..73ff98b 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -232,14 +232,18 @@ function comment_field_instance_create(FieldInstanceInterface $instance) {
     \Drupal::service('comment.manager')->addBodyField($instance->entity_type, $instance->getName());
     \Drupal::cache()->delete('comment_entity_info');
     // Assign default values for the field instance.
-    $instance->default_value = array(array(
+    if (!isset($instance->default_value)) {
+      $instance->default_value = array();
+    }
+    $instance->default_value += array(array());
+    $instance->default_value[0] += array(
       'status' => COMMENT_OPEN,
       'cid' => 0,
       'last_comment_timestamp' => 0,
       'last_comment_name' => '',
       'last_comment_uid' => 0,
       'comment_count' => 0,
-    ));
+    );
   }
 }