diff --git a/htdocs/core/class/commonobject.class.php b/htdocs/core/class/commonobject.class.php
index 24015f230cc..7a29daf0c37 100644
--- a/htdocs/core/class/commonobject.class.php
+++ b/htdocs/core/class/commonobject.class.php
@@ -167,6 +167,10 @@ abstract class CommonObject
 	 * @var CommonObject To store a cloned copy of object before to edit it and keep track of old properties
 	 */
 	public $oldcopy;
+	/**
+	 * @var CommonObject To store old value of a modified ref
+	 */
+	public $oldref;
 
 	/**
 	 * @var string		Column name of the ref field.