diff --git a/core/lib/Drupal/Core/Entity/ContentEntityBase.php b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
index fd0fe7f..619c17e 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
@@ -342,6 +342,7 @@ function __sleep() {
       }
     }
     $this->fields = array();
+    $this->fieldDefinitions = NULL;
     return array_keys(get_object_vars($this));
   }