diff --git a/modules/itop-sla-computation/model.itop-sla-computation.php b/modules/itop-sla-computation/model.itop-sla-computation.php
index 51f07fe88..490d72934 100644
--- a/modules/itop-sla-computation/model.itop-sla-computation.php
+++ b/modules/itop-sla-computation/model.itop-sla-computation.php
@@ -134,7 +134,7 @@ class SLAComputationAddOnAPI
 	 */
 	public static function GetOpenDuration($oTicket, DateTime $oStartDate, DateTime $oEndDate)
 	{
-		return abs($oEndDate->format('U') - $oStartDate-format('U'));
+		return abs($oEndDate->format('U') - $oStartDate->format('U'));
 	}
 }
 SLAComputation::SelectModule('SLAComputationAddOnAPI');