diff --git a/RIGS/migrations/0024_auto_20160229_2042.py b/RIGS/migrations/0024_auto_20160229_2042.py
new file mode 100644
index 00000000..163ff8e4
--- /dev/null
+++ b/RIGS/migrations/0024_auto_20160229_2042.py
@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('RIGS', '0023_auto_20150529_0048'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='event',
+            name='based_on',
+            field=models.ForeignKey(related_name='future_events', on_delete=django.db.models.deletion.SET_NULL, blank=True, to='RIGS.Event', null=True),
+        ),
+    ]
diff --git a/RIGS/models.py b/RIGS/models.py
index 09b3080a..fc06911f 100644
--- a/RIGS/models.py
+++ b/RIGS/models.py
@@ -301,7 +301,7 @@ class Event(models.Model, RevisionMixin):
     status = models.IntegerField(choices=EVENT_STATUS_CHOICES, default=PROVISIONAL)
     dry_hire = models.BooleanField(default=False)
     is_rig = models.BooleanField(default=True)
-    based_on = models.ForeignKey('Event', related_name='future_events', blank=True, null=True)
+    based_on = models.ForeignKey('Event', on_delete=models.SET_NULL, related_name='future_events', blank=True, null=True)
 
     # Timing
     start_date = models.DateField()
diff --git a/db.sqlite3 b/db.sqlite3
index d0e8fed8..07462b3f 100644
Binary files a/db.sqlite3 and b/db.sqlite3 differ