diff --git a/addons/mail/models/mail_message.py b/addons/mail/models/mail_message.py
index e57409ebe3e..6bd83f6427c 100644
--- a/addons/mail/models/mail_message.py
+++ b/addons/mail/models/mail_message.py
@@ -892,7 +892,7 @@ class Message(models.Model):
                 ('res_id', '=', self.res_id)
             ]).filtered(lambda fol: self.subtype_id in fol.subtype_ids)
             if self.subtype_id.internal:
-                followers.filtered(lambda fol: fol.partner_id.user_ids and group_user in fol.partner_id.user_ids[0].mapped('groups_id'))
+                followers = followers.filtered(lambda fol: fol.partner_id.user_ids and group_user in fol.partner_id.user_ids[0].mapped('groups_id'))
             channels = self_sudo.channel_ids | followers.mapped('channel_id')
             partners = self_sudo.partner_ids | followers.mapped('partner_id')
         else: