diff --git a/addons/account/controllers/mail.py b/addons/account/controllers/mail.py
index f30c69e21ba..564856b909c 100644
--- a/addons/account/controllers/mail.py
+++ b/addons/account/controllers/mail.py
@@ -11,6 +11,7 @@ from odoo.tools.misc import consteq
 
 class MailController(MailController):
 
+    @classmethod
     def _redirect_to_record(cls, model, res_id, access_token=None):
         # If the current user doesn't have access to the invoice, but provided
         # a valid access token, redirect him to the front-end view.
diff --git a/addons/sale/controllers/mail.py b/addons/sale/controllers/mail.py
index cd0701e21db..d257bfa2736 100644
--- a/addons/sale/controllers/mail.py
+++ b/addons/sale/controllers/mail.py
@@ -11,6 +11,7 @@ from odoo.tools.misc import consteq
 
 class MailController(MailController):
 
+    @classmethod
     def _redirect_to_record(cls, model, res_id, access_token=None):
         # If the current user doesn't have access to the sales order, but provided
         # a valid access token, redirect him to the front-end view.