diff -u b/lib/Drupal/pgn/Plugin/Core/Entity/PgnGame.php b/lib/Drupal/pgn/Plugin/Core/Entity/PgnGame.php
--- b/lib/Drupal/pgn/Plugin/Core/Entity/PgnGame.php
+++ b/lib/Drupal/pgn/Plugin/Core/Entity/PgnGame.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\pgn\Plugin\Core\Entity;
 
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityNG;
 use Drupal\Core\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
@@ -27,7 +28,7 @@
  *   },
  * )
  */
-class PgnGame extends EntityNG {
+class PgnGame extends EntityNG implements ContentEntityInterface {
 
   /**
    * The entity ID.