diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 172788c8517..f98b372f149 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -4926,6 +4926,7 @@ class Facture extends CommonInvoice
 
 		require_once DOL_DOCUMENT_ROOT.'/core/lib/date.lib.php';
 		require_once DOL_DOCUMENT_ROOT.'/core/class/html.formmail.class.php';
+		require_once DOL_DOCUMENT_ROOT.'/core/class/CMailFile.class.php';
 		$formmail = new FormMail($this->db);
 
 		$now = dol_now();