diff --git a/src/pretix/base/migrations/0299_fixup_eventmetaproperties.py b/src/pretix/base/migrations/0299_fixup_eventmetaproperties.py
new file mode 100644
index 0000000000..d3b4440b48
--- /dev/null
+++ b/src/pretix/base/migrations/0299_fixup_eventmetaproperties.py
@@ -0,0 +1,67 @@
+# Generated by Django 5.2.12 on 2026-04-28 11:34
+import logging
+
+from django.db import migrations
+from django.db.models import Count, F
+
+logger = logging.getLogger(__name__)
+
+
+def fix_cross_organizer_eventmetavalues(apps, schema_editor):
+    EventMetaProperty = apps.get_model("pretixbase", "EventMetaProperty")
+    EventMetaValue = apps.get_model("pretixbase", "EventMetaValue")
+
+    cross_org_values = EventMetaValue.objects.filter(event__organizer__pk__ne=F('property__organizer__pk'))
+    for emv in cross_org_values:
+        logger.info(f'Fixup {emv.event.organizer.slug}/{emv.event.slug}\n  before: {emv.property.name}({emv.property.id}@{emv.property.organizer.slug}) = {emv.value}')
+        try:
+            emv.property = emv.event.organizer.meta_properties.filter(name=emv.property.name).first()
+            logger.info(f'  found existing EventMetaProperty in {emv.event.organizer.slug}')
+        except EventMetaProperty.DoesNotExist:
+            meta_prop = emv.property
+            meta_prop.pk = None
+            meta_prop.organizer = emv.event.organizer
+            meta_prop.save(force_insert=True)
+            logger.info(f'  created new EventMetaProperty')
+            emv.property = meta_prop
+        # TODO: how to handle new duplicates in EventMetaValue.property
+        logger.info(f'  after: {emv.property.name}({emv.property.id}@{emv.property.organizer.slug}) = {emv.value}')
+        emv.save()
+
+
+def make_eventmetaproperties_unique(apps, schema_editor):
+    EventMetaProperty = apps.get_model("pretixbase", "EventMetaProperty")
+    EventMetaValue = apps.get_model("pretixbase", "EventMetaValue")
+
+    duplicates = EventMetaProperty.objects.values('organizer', 'organizer__slug', 'name').annotate(count=Count('id')).filter(count__gt=1)
+    for dup in duplicates:
+        logger.info(f'Fixup {dup['organizer__slug']} {dup['name']}')
+        props = list(EventMetaProperty.objects.filter(organizer=dup['organizer'], name=dup['name']))
+
+        # TODO: any better idea than picking the property to keep more or less randomly (first in database order)?
+        target = props[0]
+        invalid = props[1:]
+
+        # TODO: how to handle new duplicates in EventMetaValue.property
+        affected = EventMetaValue.objects.filter(
+            event__organizer=dup['organizer'], property__in=invalid
+        ).update(
+            property=target
+        )
+        logger.info(f'  Switching {affected} value(s) over to {target.name}({target.id}@{target.organizer.slug})')
+
+        for prop in invalid:
+            logger.info(f'  Deleting {prop.name}({prop.id}@{prop.organizer.slug})')
+            prop.delete()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("pretixbase", "0298_pluggable_permissions"),
+    ]
+
+    operations = [
+        migrations.RunPython(fix_cross_organizer_eventmetavalues, migrations.RunPython.noop),
+        migrations.RunPython(make_eventmetaproperties_unique, migrations.RunPython.noop),
+    ]
diff --git a/src/pretix/base/migrations/0300_alter_eventmetaproperty_unique_together.py b/src/pretix/base/migrations/0300_alter_eventmetaproperty_unique_together.py
new file mode 100644
index 0000000000..5d992fb3ca
--- /dev/null
+++ b/src/pretix/base/migrations/0300_alter_eventmetaproperty_unique_together.py
@@ -0,0 +1,17 @@
+# Generated by Django 5.2.12 on 2026-04-28 11:34
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("pretixbase", "0299_fixup_eventmetaproperties"),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name="eventmetaproperty",
+            unique_together={("organizer", "name")},
+        ),
+    ]