diff --git a/models/calendar.py b/models/calendar.py
index 700c618dece9cf81ed1872e507a96c736598af56..40a3251b5770b57a49e1f6049ea29b1e9a633f3d 100644
--- a/models/calendar.py
+++ b/models/calendar.py
@@ -33,6 +33,7 @@ class CGScopCalendar(models.Model):
         comodel_name='res.partner',
         string='Contact',
         domain=[('is_company', '=', 'True')],
+        ondelete='set null',
         default=_default_coop_id)
     project_id = fields.Many2one(
         comodel_name="project.project",