diff --git a/htdocs/core/ajax/onlineSign.php b/htdocs/core/ajax/onlineSign.php
index c3fd2e75cf8..0577ee63bea 100644
--- a/htdocs/core/ajax/onlineSign.php
+++ b/htdocs/core/ajax/onlineSign.php
@@ -59,7 +59,7 @@ $signature = GETPOST('signaturebase64');
 $ref = GETPOST('ref', 'aZ09');
 $mode = GETPOST('mode', 'aZ09');	// 'proposal', ...
 $SECUREKEY = GETPOST("securekey"); // Secure key
-$online_sign_name = GETPOST("onlinesignname");
+$online_sign_name = GETPOST("onlinesignname") ? GETPOST("onlinesignname") : '';
 
 $error = 0;
 $response = "";