diff --git a/examples/starwars/models.py b/examples/starwars/models.py
index 2f80e27..45741da 100644
--- a/examples/starwars/models.py
+++ b/examples/starwars/models.py
@@ -5,7 +5,7 @@ from django.db import models
 
 class Character(models.Model):
     name = models.CharField(max_length=50)
-    ship = models.ForeignKey('Ship', blank=True, null=True, related_name='characters')
+    ship = models.ForeignKey('Ship', on_delete=models.CASCADE, blank=True, null=True, related_name='characters')
 
     def __str__(self):
         return self.name
@@ -13,7 +13,7 @@ class Character(models.Model):
 
 class Faction(models.Model):
     name = models.CharField(max_length=50)
-    hero = models.ForeignKey(Character)
+    hero = models.ForeignKey(Character, on_delete=models.CASCADE)
 
     def __str__(self):
         return self.name
@@ -21,7 +21,7 @@ class Faction(models.Model):
 
 class Ship(models.Model):
     name = models.CharField(max_length=50)
-    faction = models.ForeignKey(Faction, related_name='ships')
+    faction = models.ForeignKey(Faction, on_delete=models.CASCADE, related_name='ships')
 
     def __str__(self):
         return self.name
diff --git a/graphene_django/tests/models.py b/graphene_django/tests/models.py
index 0c62f28..db1fca4 100644
--- a/graphene_django/tests/models.py
+++ b/graphene_django/tests/models.py
@@ -15,7 +15,7 @@ class Pet(models.Model):
 
 class FilmDetails(models.Model):
     location = models.CharField(max_length=30)
-    film = models.OneToOneField('Film', related_name='details')
+    film = models.OneToOneField('Film', on_delete=models.CASCADE, related_name='details')
 
 
 class Film(models.Model):
@@ -37,8 +37,8 @@ class Reporter(models.Model):
 class Article(models.Model):
     headline = models.CharField(max_length=100)
     pub_date = models.DateField()
-    reporter = models.ForeignKey(Reporter, related_name='articles')
-    editor = models.ForeignKey(Reporter, related_name='edited_articles_+')
+    reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE, related_name='articles')
+    editor = models.ForeignKey(Reporter, on_delete=models.CASCADE, related_name='edited_articles_+')
     lang = models.CharField(max_length=2, help_text='Language', choices=[
         ('es', 'Spanish'),
         ('en', 'English')