diff --git a/vendor/symposion/proposals/models.py b/vendor/symposion/proposals/models.py
index 08120eca852b473430d9664ab8bdb250ee202288..bc3f295e7c6df33d2bde613033d4625f49aa1a10 100644
--- a/vendor/symposion/proposals/models.py
+++ b/vendor/symposion/proposals/models.py
@@ -1,13 +1,13 @@
 import os
 import uuid
 
-from django.core.urlresolvers import reverse
 from django.db import models
 from django.db.models import Q
+from django.urls import reverse
 from django.utils.translation import ugettext_lazy as _
 from django.utils.timezone import now
 
-from django.contrib.auth.models import User
+from django.contrib.auth import get_user_model
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError
 
@@ -19,6 +19,8 @@ from symposion.text_parser import parse
 from symposion.conference.models import Section
 from symposion.speakers.models import Speaker
 
+User = get_user_model()
+
 
 class ProposalSection(models.Model):
     """
@@ -30,7 +32,11 @@ class ProposalSection(models.Model):
       * closed is NULL or False
     """
 
-    section = models.OneToOneField(Section, verbose_name=_("Section"))
+    section = models.OneToOneField(
+        Section,
+        verbose_name=_("Section"),
+        on_delete=models.CASCADE,
+    )
 
     start = models.DateTimeField(null=True, blank=True, verbose_name=_("Start"))
     end = models.DateTimeField(null=True, blank=True, verbose_name=_("End"))
@@ -66,7 +72,12 @@ class ProposalKind(models.Model):
     to distinguish the section as well as the kind.
     """
 
-    section = models.ForeignKey(Section, related_name="proposal_kinds", verbose_name=_("Section"))
+    section = models.ForeignKey(
+        Section,
+        related_name="proposal_kinds",
+        verbose_name=_("Section"),
+        on_delete=models.CASCADE,
+    )
 
     name = models.CharField(_("Name"), max_length=100)
     slug = models.SlugField(verbose_name=_("Slug"))
@@ -79,7 +90,11 @@ class ProposalBase(models.Model):
 
     objects = InheritanceManager()
 
-    kind = models.ForeignKey(ProposalKind, verbose_name=_("Kind"))
+    kind = models.ForeignKey(
+        ProposalKind,
+        verbose_name=_("Kind"),
+        on_delete=models.CASCADE,
+    )
 
     title = models.CharField(max_length=100, verbose_name=_("Title"))
     abstract = models.TextField(
@@ -134,7 +149,12 @@ class ProposalBase(models.Model):
         editable=False,
         verbose_name=_("Submitted")
     )
-    speaker = models.ForeignKey(Speaker, related_name="proposals", verbose_name=_("Speaker"))
+    speaker = models.ForeignKey(
+        Speaker,
+        related_name="proposals",
+        verbose_name=_("Speaker"),
+        on_delete=models.CASCADE,
+    )
 
     # @@@ this validation used to exist as a validators keyword on additional_speakers
     #     M2M field but that is no longer supported by Django. Should be moved to
@@ -213,8 +233,16 @@ class AdditionalSpeaker(models.Model):
         (SPEAKING_STATUS_DECLINED, _("Declined")),
     ]
 
-    speaker = models.ForeignKey(Speaker, verbose_name=_("Speaker"))
-    proposalbase = models.ForeignKey(ProposalBase, verbose_name=_("Proposalbase"))
+    speaker = models.ForeignKey(
+        Speaker,
+        verbose_name=_("Speaker"),
+        on_delete=models.CASCADE,
+    )
+    proposalbase = models.ForeignKey(
+        ProposalBase,
+        verbose_name=_("Proposalbase"),
+        on_delete=models.CASCADE,
+    )
     status = models.IntegerField(choices=SPEAKING_STATUS, default=SPEAKING_STATUS_PENDING, verbose_name=_("Status"))
 
     class Meta:
@@ -239,9 +267,18 @@ def uuid_filename(instance, filename):
 
 class SupportingDocument(models.Model):
 
-    proposal = models.ForeignKey(ProposalBase, related_name="supporting_documents", verbose_name=_("Proposal"))
+    proposal = models.ForeignKey(
+        ProposalBase,
+        related_name="supporting_documents",
+        verbose_name=_("Proposal"),
+        on_delete=models.CASCADE,
+    )
 
-    uploaded_by = models.ForeignKey(User, verbose_name=_("Uploaded by"))
+    uploaded_by = models.ForeignKey(
+        User,
+        verbose_name=_("Uploaded by"),
+        on_delete=models.CASCADE,
+    )
 
     created_at = models.DateTimeField(default=now, verbose_name=_("Created at"))