diff --git a/vendor/symposion/speakers/models.py b/vendor/symposion/speakers/models.py
index f3da835cffd7bae2be8fe6eb631fead065befcae..18fa64039cb126e230fa8f3ec911ed65cd7d6f7c 100644
--- a/vendor/symposion/speakers/models.py
+++ b/vendor/symposion/speakers/models.py
@@ -1,18 +1,26 @@
 import datetime
 
-from django.core.urlresolvers import reverse
 from django.db import models
+from django.urls import reverse
 from django.utils.translation import ugettext_lazy as _
 
-from django.contrib.auth.models import User
+from django.contrib.auth import get_user_model
 
 from symposion import constants
 from symposion.text_parser import parse
 
+User = get_user_model()
+
 
 class Speaker(models.Model):
 
-    user = models.OneToOneField(User, null=True, related_name="speaker_profile", verbose_name=_("User"))
+    user = models.OneToOneField(
+        User,
+        null=True,
+        related_name="speaker_profile",
+        verbose_name=_("User"),
+        on_delete=models.CASCADE,
+    )
     name = models.CharField(verbose_name=_("Name"), max_length=100,
                             help_text=_("As you would like it to appear in the"
                                         " conference programme."))