diff --git a/addons/mail/views/mail_activity_views.xml b/addons/mail/views/mail_activity_views.xml
index 500750b6c72..71bc3592c3d 100644
--- a/addons/mail/views/mail_activity_views.xml
+++ b/addons/mail/views/mail_activity_views.xml
@@ -15,7 +15,7 @@
                         <group name="activity_details">
                             <field name="active" invisible="1"/>
                             <field name="category"/>
-                            <field name="default_user_id" widget="selection" domain="[('share', '=', False)]"/>
+                            <field name="default_user_id" options="{'no_create': True, 'no_edit': True}" domain="[('share', '=', False)]"/>
                             <field name="res_model_id" groups="base.group_no_one"/>
                             <field name="res_model_change" invisible="1"/>
                             <field name="initial_res_model_id" invisible="1"/>