diff --git a/inc/abstractcontainerinstance.class.php b/inc/abstractcontainerinstance.class.php
index d590bb53..87ebcbd5 100644
--- a/inc/abstractcontainerinstance.class.php
+++ b/inc/abstractcontainerinstance.class.php
@@ -33,6 +33,8 @@ abstract class PluginFieldsAbstractContainerInstance extends CommonDBChild
     public static $itemtype = 'itemtype';
     public static $items_id = 'items_id';
 
+    public static $mustBeAttached     = false;
+
     /**
      * This function relies on the static property `static::$plugins_forward_entity`,
      * which should be populated using the following method (from setup):