diff --git a/htdocs/core/class/commoninvoice.class.php b/htdocs/core/class/commoninvoice.class.php
index 0314bf34413..5c9d6257fb9 100644
--- a/htdocs/core/class/commoninvoice.class.php
+++ b/htdocs/core/class/commoninvoice.class.php
@@ -253,6 +253,7 @@ abstract class CommonInvoice extends CommonObject
 		}
 		if ($mode == 4)
 		{
+			$prefix='';
 			if (! $paye)
 			{
 				if ($status == 0) return img_picto($langs->trans('BillStatusDraft'),'statut0').' '.$langs->trans('BillStatusDraft');