diff --git a/taiga/projects/epics/migrations/0003_auto_20160901_1021.py b/taiga/projects/epics/migrations/0003_auto_20160901_1021.py
new file mode 100644
index 00000000..e23169f2
--- /dev/null
+++ b/taiga/projects/epics/migrations/0003_auto_20160901_1021.py
@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.2 on 2016-09-01 10:21
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('epics', '0002_epic_color'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='relateduserstory',
+            unique_together=set([('user_story', 'epic')]),
+        ),
+    ]
diff --git a/taiga/projects/epics/models.py b/taiga/projects/epics/models.py
index 3d1a2ce4..64bdbb84 100644
--- a/taiga/projects/epics/models.py
+++ b/taiga/projects/epics/models.py
@@ -103,6 +103,7 @@ class RelatedUserStory(models.Model):
         verbose_name = "related user story"
         verbose_name_plural = "related user stories"
         ordering = ["user_story", "order", "id"]
+        unique_together = (("user_story", "epic"), )
 
     def __str__(self):
         return "{0} - {1}".format(self.epic_id, self.user_story_id)