diff --git a/htdocs/core/triggers/interface_20_modWorkflow_WorkflowManager.class.php b/htdocs/core/triggers/interface_20_modWorkflow_WorkflowManager.class.php
index 6599bd2ba58..85643206762 100644
--- a/htdocs/core/triggers/interface_20_modWorkflow_WorkflowManager.class.php
+++ b/htdocs/core/triggers/interface_20_modWorkflow_WorkflowManager.class.php
@@ -241,7 +241,7 @@ class InterfaceWorkflowManager extends DolibarrTriggers
 			// First classify billed the order to allow the proposal classify process
 			if (isModEnabled('order') && isModEnabled('workflow') && getDolGlobalString('WORKFLOW_SUM_INVOICES_AMOUNT_CLASSIFY_BILLED_ORDER')) {
 				$object->fetchObjectLinked('', 'commande', $object->id, $object->element);
-				if (count($object->linkedObjects['commande']) == 1) {	// If the invoice has only 1 source order
+				if (!empty($object->linkedObjects['commande']) && count($object->linkedObjects['commande']) == 1) {	// If the invoice has only 1 source order
 					$orderLinked = reset($object->linkedObjects['commande']);
 					$orderLinked->fetchObjectLinked($orderLinked->id, '', $orderLinked->element);
 					if (count($orderLinked->linkedObjects['facture']) >= 1) {