diff --git a/billard/migrations/0021_accounting_account_user.py b/billard/migrations/0021_accounting_account_user.py
index 789da72..08094d5 100644
--- a/billard/migrations/0021_accounting_account_user.py
+++ b/billard/migrations/0021_accounting_account_user.py
@@ -1,9 +1,10 @@
 # -*- coding: utf-8 -*-
-# Generated by Django 1.11 on 2017-04-26 09:57
+# Generated by Django 1.11 on 2017-04-26 10:14
 from __future__ import unicode_literals
 
 from django.conf import settings
 from django.db import migrations, models
+import django.db.models.deletion
 
 
 class Migration(migrations.Migration):
@@ -17,6 +18,6 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='accounting',
             name='account_user',
-            field=models.ManyToManyField(related_name='accountings', to=settings.AUTH_USER_MODEL, verbose_name='Abr. Benutzer'),
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='accountings', to=settings.AUTH_USER_MODEL, verbose_name='Abr. Benutzer'),
         ),
     ]
diff --git a/billard/models.py b/billard/models.py
index f343e24..8360638 100644
--- a/billard/models.py
+++ b/billard/models.py
@@ -85,7 +85,7 @@ class Accounting(models.Model):
     reporter_uuid = models.UUIDField(blank=True, null=True, verbose_name='Reporter UUID')
     prize_normal = models.DecimalField(max_digits=5, decimal_places=2, blank=True, null=True, verbose_name="Preis Normalzeit")
     prize_hh = models.DecimalField(max_digits=5, decimal_places=2, blank=True, null=True, verbose_name="Preis Happy Hour")
-    account_user = models.ManyToManyField(User, related_name='accountings', verbose_name="Abr. Benutzer")
+    account_user = models.OneToOneField(User, related_name='accountings', verbose_name="Abr. Benutzer", blank=True, null=True)
 
     def __str__(self):
         return '{}: {} -> {}, {}, {}'.format(self.desk, self.time_from, self.time_to, self.prize, self.billed)