diff --git a/src/pretix/base/migrations/0278_login_source_add_unique_together.py b/src/pretix/base/migrations/0278_login_source_add_unique_together.py
new file mode 100644
index 0000000000..028c358843
--- /dev/null
+++ b/src/pretix/base/migrations/0278_login_source_add_unique_together.py
@@ -0,0 +1,41 @@
+# Generated by Django 4.2.16 on 2025-02-28 13:25
+
+from django.db import migrations, models
+
+
+def remove_duplicates(apps, schema_editor):
+    UserKnownLoginSource = apps.get_model("pretixbase", "UserKnownLoginSource")
+    unique_fields = ["user", "agent_type", "device_type", "os_type", "country"]
+
+    duplicates = (
+        UserKnownLoginSource.objects
+        .values(*unique_fields)
+        .order_by()
+        .annotate(latest_id=models.Max('id'), count=models.Count('id'))
+        .filter(count__gt=1)
+    )
+
+    for duplicate in duplicates:
+        (
+            UserKnownLoginSource.objects
+            .filter(**{x: duplicate[x] for x in unique_fields})
+            .exclude(id=duplicate["latest_id"])
+            .delete()
+        )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("pretixbase", "0277_customerssoclient_require_pkce_and_more"),
+    ]
+
+    operations = [
+        migrations.RunPython(remove_duplicates, migrations.RunPython.noop),
+        migrations.AlterUniqueTogether(
+            name="userknownloginsource",
+            unique_together={
+                ("user", "agent_type", "device_type", "os_type", "country")
+            },
+        ),
+    ]
diff --git a/src/pretix/base/models/auth.py b/src/pretix/base/models/auth.py
index 297316e942..27e0ee6961 100644
--- a/src/pretix/base/models/auth.py
+++ b/src/pretix/base/models/auth.py
@@ -602,6 +602,9 @@ class UserKnownLoginSource(models.Model):
     country = FastCountryField(null=True, blank=True)
     last_seen = models.DateTimeField()
 
+    class Meta:
+        unique_together = ('user', 'agent_type', 'device_type', 'os_type', 'country')
+
 
 class StaffSession(models.Model):
     user = models.ForeignKey('User', on_delete=models.PROTECT)