diff --git a/core/metamodel.class.php b/core/metamodel.class.php
index aa08fb292..399379f90 100644
--- a/core/metamodel.class.php
+++ b/core/metamodel.class.php
@@ -536,7 +536,10 @@ abstract class MetaModel
 	 */
 	final static public function GetUniquenessRules($sClass)
 	{
-		self::_check_subclass($sClass);
+		if (!isset(self::$m_aClassParams[$sClass]))
+		{
+			return array();
+		}
 
 		$aCurrentUniquenessRules = array();