diff --git a/setup/modelfactory.class.inc.php b/setup/modelfactory.class.inc.php
index b9a2fd355..49d3eebab 100644
--- a/setup/modelfactory.class.inc.php
+++ b/setup/modelfactory.class.inc.php
@@ -488,6 +488,9 @@ class ModelFactory
 			}
 			$oTargetNode->Delete();
 			break;
+			
+		default:
+			throw new Exception(MFDocument::GetItopNodePath($oSourceNode).' at line '.$oSourceNode->getLineNo().": unexpected value for attribute _delta: '".$oSourceNode->getAttribute('_delta')."'");
 		}
 
 		if ($oSourceNode->hasAttribute('_rename_from'))