diff --git a/addons/mail/mail_thread.py b/addons/mail/mail_thread.py
index 0029dc7ca9f..788854891c9 100644
--- a/addons/mail/mail_thread.py
+++ b/addons/mail/mail_thread.py
@@ -706,7 +706,7 @@ class mail_thread(osv.AbstractModel):
         """ Wrapper on message_subscribe, using users. If user_ids is not
             provided, subscribe uid instead. """
         if not user_ids:
-            user_ids = [uid]
+            return False
         partner_ids = [user.partner_id.id for user in self.pool.get('res.users').browse(cr, uid, user_ids, context=context)]
         return self.message_subscribe(cr, uid, ids, partner_ids, subtype_ids=subtype_ids, context=context)