--- a/src/notes/models/auth.py	Tue Jul 10 15:18:03 2018 +0200
+++ b/src/notes/models/auth.py	Wed Jul 18 17:32:09 2018 +0200
@@ -20,7 +20,8 @@
     default_group = models.ForeignKey(
         Group,
         null=False,
-        verbose_name=_("UserProfile|default_group"))
+        verbose_name=_("UserProfile|default_group"),
+        on_delete=models.PROTECT)
 
     class Meta:
         verbose_name = _('UserProfile')