diff --git a/vendor/symposion/teams/models.py b/vendor/symposion/teams/models.py
index ca197272fb89fc474139247064286fcea7e0cf72..a09abad8b03b1b80809695d9810bac1502f05c5d 100644
--- a/vendor/symposion/teams/models.py
+++ b/vendor/symposion/teams/models.py
@@ -2,11 +2,15 @@ import datetime
 
 from django.db import models
 from django.utils.translation import ugettext_lazy as _
+from django.urls import reverse
 
-from django.contrib.auth.models import Permission, User
+from django.contrib.auth.models import Permission
+from django.contrib.auth import get_user_model
 
 from reversion import revisions as reversion
 
+User = get_user_model()
+
 
 TEAM_ACCESS_CHOICES = [
     ("open", _("open")),
@@ -36,9 +40,8 @@ class Team(models.Model):
     created = models.DateTimeField(default=datetime.datetime.now,
                                    editable=False, verbose_name=_("Created"))
 
-    @models.permalink
     def get_absolute_url(self):
-        return ("team_detail", [self.slug])
+        return reverse("team_detail", args=[self.slug])
 
     def __str__(self):
         return self.name
@@ -78,10 +81,18 @@ MEMBERSHIP_STATE_CHOICES = [
 
 class Membership(models.Model):
 
-    user = models.ForeignKey(User, related_name="memberships",
-                             verbose_name=_("User"))
-    team = models.ForeignKey(Team, related_name="memberships",
-                             verbose_name=_("Team"))
+    user = models.ForeignKey(
+        User,
+        related_name="memberships",
+        verbose_name=_("User"),
+        on_delete=models.CASCADE,
+    )
+    team = models.ForeignKey(
+        Team,
+        related_name="memberships",
+        verbose_name=_("Team"),
+        on_delete=models.CASCADE,
+    )
     state = models.CharField(max_length=20, choices=MEMBERSHIP_STATE_CHOICES,
                              verbose_name=_("State"))
     message = models.TextField(blank=True, verbose_name=_("Message"))