diff --git a/htdocs/core/actions_sendmails.inc.php b/htdocs/core/actions_sendmails.inc.php
index 4f7580bb8ca..e459437a74e 100644
--- a/htdocs/core/actions_sendmails.inc.php
+++ b/htdocs/core/actions_sendmails.inc.php
@@ -190,7 +190,7 @@ if (($action == 'send' || $action == 'relance') && !GETPOST('addfile') && !GETPO
 			$tmparray[] = trim(GETPOST('sendto', 'alphawithlgt'));
 		}
 
-		if (trim($_POST['tomail'])) {
+		if (isset($_POST['tomail']) && trim($_POST['tomail'])) {
 			// Recipients are provided into free hidden text field
 			$tmparray[] = trim(GETPOST('tomail', 'alphawithlgt'));
 		}