diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 84db8a44be2..e9b6e54ee67 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -5810,9 +5810,9 @@ class Facture extends CommonInvoice
 							$joinFileName = [];
 							$joinFileMime = [];
 							if ($arraymessage->joinfiles == 1 && !empty($tmpinvoice->last_main_doc)) {
-								$joinFile[] = DOL_DATA_ROOT.$tmpinvoice->last_main_doc;
+								$joinFile[] = DOL_DATA_ROOT.'/'.$tmpinvoice->last_main_doc;
 								$joinFileName[] = basename($tmpinvoice->last_main_doc);
-								$joinFileMime[] = dol_mimetype(DOL_DATA_ROOT.$tmpinvoice->last_main_doc);
+								$joinFileMime[] = dol_mimetype(DOL_DATA_ROOT.'/'.$tmpinvoice->last_main_doc);
 							}
 
 							// Mail Creation