diff --git a/addons/mail/mail_message.py b/addons/mail/mail_message.py
index ac68a4bfd7f..d3eebeb1af0 100644
--- a/addons/mail/mail_message.py
+++ b/addons/mail/mail_message.py
@@ -795,7 +795,7 @@ class mail_message(osv.Model):
     def _invalidate_documents(self):
         """ Invalidate the cache of the documents followed by ``self``. """
         for record in self:
-            if record.res_id:
+            if record.model and record.res_id:
                 self.env[record.model].invalidate_cache(ids=[record.res_id])
 
     def create(self, cr, uid, values, context=None):