diff --git a/users/migrations/0004_alter_userorigin_origin_id.py b/users/migrations/0004_alter_userorigin_origin_id.py
new file mode 100644
index 00000000..e885a288
--- /dev/null
+++ b/users/migrations/0004_alter_userorigin_origin_id.py
@@ -0,0 +1,21 @@
+# Generated by Django 4.2.13 on 2024-07-25 09:41
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("users", "0003_userorigin"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="userorigin",
+            name="origin_id",
+            field=models.CharField(
+                blank=True, default="", max_length=100, verbose_name="Origin ID"
+            ),
+            preserve_default=False,
+        ),
+    ]
diff --git a/users/models.py b/users/models.py
index 1dd9cec3..d3cc99c8 100644
--- a/users/models.py
+++ b/users/models.py
@@ -35,7 +35,7 @@ class UserOrigin(models.Model):
     user = models.ForeignKey(User, related_name="origins", on_delete=models.CASCADE)
     data_source = models.ForeignKey("hours.DataSource", on_delete=models.CASCADE)
     origin_id = models.CharField(
-        verbose_name=_("Origin ID"), max_length=100, null=True, blank=True
+        verbose_name=_("Origin ID"), max_length=100, blank=True
     )
 
     class Meta:
diff --git a/users/tests/conftest.py b/users/tests/conftest.py
new file mode 100644
index 00000000..c0752e4e
--- /dev/null
+++ b/users/tests/conftest.py
@@ -0,0 +1,6 @@
+from pytest_factoryboy import register
+
+from hours.tests.conftest import DataSourceFactory, UserFactory
+
+register(UserFactory)
+register(DataSourceFactory)
diff --git a/users/tests/test_models.py b/users/tests/test_models.py
new file mode 100644
index 00000000..5f5d9546
--- /dev/null
+++ b/users/tests/test_models.py
@@ -0,0 +1,14 @@
+import pytest
+from django.db import IntegrityError
+
+from users.models import UserOrigin
+
+
+@pytest.mark.django_db
+def test_user_origin_shouldnt_allow_duplicate_empty_origin_id(user, data_source):
+    """Duplicate UserOrigin instances shouldn't get created when data source is
+    the same but origin_id is empty.
+    """
+    UserOrigin.objects.create(user=user, data_source=data_source)
+    with pytest.raises(IntegrityError):
+        UserOrigin.objects.create(user=user, data_source=data_source)