diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 17cc796ff97..7c1aabdf072 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -818,7 +818,7 @@ class Facture extends CommonInvoice
 
 						// Complete vat rate with code
 						$vatrate = $newinvoiceline->tva_tx;
-						if ($newinvoiceline->vat_src_code && ! preg_match('/\(.*\)/', $vatrate)) {
+						if ($newinvoiceline->vat_src_code && ! preg_match('/\(.*\)/', (string) $vatrate)) {
 							$vatrate .= ' ('.$newinvoiceline->vat_src_code.')';
 						}