diff --git a/setup/itopdesignformat.class.inc.php b/setup/itopdesignformat.class.inc.php
index a86c5b367..922b3a2a7 100644
--- a/setup/itopdesignformat.class.inc.php
+++ b/setup/itopdesignformat.class.inc.php
@@ -519,6 +519,15 @@ class iTopDesignFormat
 			$this->LogWarning('The attribute '.self::GetItopNodePath($oNode).' is irrelevant and must be removed.');
 			$this->DeleteNode($oNode);
 		}
+
+		// Discard _delta="if_exists"
+		//
+		$oNodeList = $oXPath->query("//*[@_delta='if_exists']");
+		foreach ($oNodeList as $oNode)
+		{
+			$this->LogWarning('The flag _delta="if_exists" on '.self::GetItopNodePath($oNode).' is irrelevant and must be replaced by _delta="must_exist".');
+			$oNode->setAttribute('_delta', 'must_exist');
+		}
 	}
 
 	/**