diff --git a/CHANGELOG.md b/CHANGELOG.md
index c02a4bbf..981803c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,13 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
+## Unreleased
+
+### Improvements
+- Database schema: set Check.user to not null
+- Database schema: add uniqueness constraint to Check.code
+
+
 ## 1.4.0 - 2018-12-25
 
 ### Improvements
diff --git a/hc/api/management/commands/prunepingsslow.py b/hc/api/management/commands/prunepingsslow.py
index 1ceabf85..c1700412 100644
--- a/hc/api/management/commands/prunepingsslow.py
+++ b/hc/api/management/commands/prunepingsslow.py
@@ -20,7 +20,7 @@ class Command(BaseCommand):
         for user in User.objects.filter(profile=None):
             Profile.objects.get_or_create(user_id=user.id)
 
-        checks = Check.objects.filter(user__isnull=False)
+        checks = Check.objects
         checks = checks.annotate(limit=F("user__profile__ping_log_limit"))
 
         for check in checks:
diff --git a/hc/api/migrations/0048_auto_20190102_0737.py b/hc/api/migrations/0048_auto_20190102_0737.py
new file mode 100644
index 00000000..d636f261
--- /dev/null
+++ b/hc/api/migrations/0048_auto_20190102_0737.py
@@ -0,0 +1,19 @@
+# Generated by Django 2.1.4 on 2019-01-02 07:37
+
+from django.db import migrations
+
+
+def remove_anon_checks(apps, schema_editor):
+    Check = apps.get_model("api", "Check")
+    Check.objects.filter(user=None).delete()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0047_auto_20181225_2315'),
+    ]
+
+    operations = [
+        migrations.RunPython(remove_anon_checks, migrations.RunPython.noop),
+    ]
diff --git a/hc/api/migrations/0049_auto_20190102_0743.py b/hc/api/migrations/0049_auto_20190102_0743.py
new file mode 100644
index 00000000..e3db9b0a
--- /dev/null
+++ b/hc/api/migrations/0049_auto_20190102_0743.py
@@ -0,0 +1,26 @@
+# Generated by Django 2.1.4 on 2019-01-02 07:43
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+import uuid
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0048_auto_20190102_0737'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='check',
+            name='code',
+            field=models.UUIDField(default=uuid.uuid4, editable=False, unique=True),
+        ),
+        migrations.AlterField(
+            model_name='check',
+            name='user',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL),
+        ),
+    ]
diff --git a/hc/api/models.py b/hc/api/models.py
index aa9ff5b7..6dab0c88 100644
--- a/hc/api/models.py
+++ b/hc/api/models.py
@@ -64,9 +64,9 @@ def isostring(dt):
 class Check(models.Model):
     name = models.CharField(max_length=100, blank=True)
     tags = models.CharField(max_length=500, blank=True)
-    code = models.UUIDField(default=uuid.uuid4, editable=False, db_index=True)
+    code = models.UUIDField(default=uuid.uuid4, editable=False, unique=True)
     desc = models.TextField(blank=True)
-    user = models.ForeignKey(User, models.CASCADE, blank=True, null=True)
+    user = models.ForeignKey(User, models.CASCADE)
     created = models.DateTimeField(auto_now_add=True)
     kind = models.CharField(max_length=10, default="simple",
                             choices=CHECK_KINDS)
diff --git a/hc/api/tests/test_check_model.py b/hc/api/tests/test_check_model.py
index 858e3954..ea0ee595 100644
--- a/hc/api/tests/test_check_model.py
+++ b/hc/api/tests/test_check_model.py
@@ -1,11 +1,11 @@
 from datetime import datetime, timedelta
 
-from django.test import TestCase
 from django.utils import timezone
 from hc.api.models import Check
+from hc.test import BaseTestCase
 
 
-class CheckModelTestCase(TestCase):
+class CheckModelTestCase(BaseTestCase):
 
     def test_it_strips_tags(self):
         check = Check()
@@ -155,11 +155,12 @@ class CheckModelTestCase(TestCase):
         dt = timezone.make_aware(datetime(2000, 1, 1), timezone=timezone.utc)
 
         # Expect ping every round hour
-        check = Check()
+        check = Check(user=self.alice)
         check.kind = "cron"
         check.schedule = "0 * * * *"
         check.status = "up"
         check.last_ping = dt
+        # Need to save it for M2M relations to work:
         check.save()
 
         d = check.to_dict()
diff --git a/hc/api/tests/test_ping.py b/hc/api/tests/test_ping.py
index 193318ce..1d3223f1 100644
--- a/hc/api/tests/test_ping.py
+++ b/hc/api/tests/test_ping.py
@@ -1,15 +1,16 @@
 from datetime import timedelta as td
 
-from django.test import Client, TestCase
+from django.test import Client
 from django.utils.timezone import now
 from hc.api.models import Check, Flip, Ping
+from hc.test import BaseTestCase
 
 
-class PingTestCase(TestCase):
+class PingTestCase(BaseTestCase):
 
     def setUp(self):
-        super(PingTestCase, self).setUp()
-        self.check = Check.objects.create()
+        super().setUp()
+        self.check = Check.objects.create(user=self.alice)
 
     def test_it_works(self):
         r = self.client.get("/ping/%s/" % self.check.code)
diff --git a/hc/front/tests/test_ping_details.py b/hc/front/tests/test_ping_details.py
index 3c9108ad..1b26e8b1 100644
--- a/hc/front/tests/test_ping_details.py
+++ b/hc/front/tests/test_ping_details.py
@@ -34,11 +34,6 @@ class LastPingTestCase(BaseTestCase):
         r = self.client.get("/checks/%s/last_ping/" % check.code)
         self.assertContains(r, "/start", status_code=200)
 
-    def test_it_requires_user(self):
-        check = Check.objects.create()
-        r = self.client.get("/checks/%s/last_ping/" % check.code)
-        self.assertEqual(r.status_code, 404)
-
     def test_it_accepts_n(self):
         check = Check(user=self.alice)
         check.save()