diff --git a/addons/mail/models/mail_message.py b/addons/mail/models/mail_message.py
index 5120e3fe624..1339f9fe5c9 100644
--- a/addons/mail/models/mail_message.py
+++ b/addons/mail/models/mail_message.py
@@ -1160,7 +1160,7 @@ class Message(models.Model):
         for record in self:
             model = model or record.model
             res_id = res_id or record.res_id
-            if issubclass(self.pool[model], self.pool['mail.thread']):
+            if model in self.pool and issubclass(self.pool[model], self.pool['mail.thread']):
                 self.env[model].browse(res_id).invalidate_recordset(fnames)
 
     def _get_search_domain_share(self):