diff --git a/core/modules/comment/src/Plugin/Field/FieldType/CommentItem.php b/core/modules/comment/src/Plugin/Field/FieldType/CommentItem.php
index c9e23e9..173594e 100644
--- a/core/modules/comment/src/Plugin/Field/FieldType/CommentItem.php
+++ b/core/modules/comment/src/Plugin/Field/FieldType/CommentItem.php
@@ -159,6 +159,13 @@ public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  public static function mainPropertyName() {
+    return 'cid';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function isEmpty() {
     // There is always a value for this field, it is one of
     // CommentItemInterface::OPEN, CommentItemInterface::CLOSED or