diff --git a/httpproxy/migrations/0001_initial.py b/httpproxy/migrations/0001_initial.py
index ef6e988..d2a9333 100644
--- a/httpproxy/migrations/0001_initial.py
+++ b/httpproxy/migrations/0001_initial.py
@@ -36,7 +36,7 @@ class Migration(migrations.Migration):
                 ('order', models.PositiveSmallIntegerField(default=1)),
                 ('name', models.CharField(max_length=100, verbose_name='naam')),
                 ('value', models.CharField(max_length=250, null=True, verbose_name='value', blank=True)),
-                ('request', models.ForeignKey(related_name='parameters', verbose_name='request', to='httpproxy.Request')),
+                ('request', models.ForeignKey(related_name='parameters', verbose_name='request', to='httpproxy.Request', on_delete=models.CASCADE)),
             ],
             options={
                 'ordering': ('order',),
@@ -52,7 +52,7 @@ class Migration(migrations.Migration):
                 ('status', models.PositiveSmallIntegerField(default=200)),
                 ('content_type', models.CharField(max_length=200, verbose_name='inhoudstype')),
                 ('content', models.TextField(verbose_name='inhoud')),
-                ('request', models.OneToOneField(verbose_name='request', to='httpproxy.Request')),
+                ('request', models.OneToOneField(verbose_name='request', to='httpproxy.Request', on_delete=models.CASCADE)),
             ],
             options={
                 'verbose_name': 'response',
diff --git a/httpproxy/models.py b/httpproxy/models.py
index c09c12c..3081742 100644
--- a/httpproxy/models.py
+++ b/httpproxy/models.py
@@ -1,5 +1,5 @@
 from django.db import models
-from django.utils.six.moves import urllib
+from six.moves import urllib
 from django.utils.translation import ugettext as _
 
 
@@ -68,7 +68,7 @@ class RequestParameter(models.Model):
         ('G', 'GET'),
         ('P', 'POST'),
     )
-    request = models.ForeignKey(Request, verbose_name=_('request'), related_name='parameters')
+    request = models.ForeignKey(Request, verbose_name=_('request'), related_name='parameters', on_delete=models.CASCADE)
     type = models.CharField(max_length=1, choices=REQUEST_TYPES, default='G')
     order = models.PositiveSmallIntegerField(default=1)
     name = models.CharField(_('name'), max_length=100)
@@ -89,7 +89,7 @@ class Response(models.Model):
     The response that was recorded in response to the corresponding
     :class:`~httpproxy.models.Request`.
     """
-    request = models.OneToOneField(Request, verbose_name=_('request'))
+    request = models.OneToOneField(Request, verbose_name=_('request'), on_delete=models.CASCADE)
     status = models.PositiveSmallIntegerField(default=200)
     content_type = models.CharField(_('content type'), max_length=200)
     content = models.TextField(_('content'))
diff --git a/httpproxy/views.py b/httpproxy/views.py
index 6b65cb0..d48004b 100644
--- a/httpproxy/views.py
+++ b/httpproxy/views.py
@@ -3,7 +3,7 @@
 import re
 
 from django.http import HttpResponse
-from django.utils.six.moves import urllib
+from six.moves import urllib
 from django.views.generic import View
 
 from httpproxy.recorder import ProxyRecorder