diff --git a/htdocs/core/class/commondocgenerator.class.php b/htdocs/core/class/commondocgenerator.class.php
index f6725c6aef1..5799a1607e9 100644
--- a/htdocs/core/class/commondocgenerator.class.php
+++ b/htdocs/core/class/commondocgenerator.class.php
@@ -452,7 +452,7 @@ abstract class CommonDocGenerator
 			$array_key.'_ref_ext' => (property_exists($object, 'ref_ext') ? $object->ref_ext : ''),
 			$array_key.'_ref_customer'=>(!empty($object->ref_client) ? $object->ref_client : (empty($object->ref_customer) ? '' : $object->ref_customer)),
 			$array_key.'_ref_supplier'=>(!empty($object->ref_fournisseur) ? $object->ref_fournisseur : (empty($object->ref_supplier) ? '' : $object->ref_supplier)),
-			$array_key.'_source_invoice_ref'=>(!empty($invoice_source->ref) ? $invoice_source->ref : (empty($invoice_source->ref) ? '' : $invoice_source->ref)),
+			$array_key.'_source_invoice_ref'=>((empty($invoice_source) || empty($invoice_source->ref)) ? '' : $invoice_source->ref),
 			// Dates
 			$array_key.'_hour'=>dol_print_date($date, 'hour'),
 			$array_key.'_date'=>dol_print_date($date, 'day'),