diff --git a/backend/src/core/identity-migration/migrations/001_migrate_user_id_to_uuid.sql b/backend/src/core/identity-migration/migrations/001_migrate_user_id_to_uuid.sql
index 230a3b2..95d9d74 100644
--- a/backend/src/core/identity-migration/migrations/001_migrate_user_id_to_uuid.sql
+++ b/backend/src/core/identity-migration/migrations/001_migrate_user_id_to_uuid.sql
@@ -90,6 +90,14 @@ DELETE FROM user_preferences
     AND user_id ~ '^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$'
     AND NOT EXISTS (SELECT 1 FROM user_profiles WHERE id = user_preferences.user_id::uuid);
 
+-- Deduplicate user_preferences: same user may have both an auth0_sub row and
+-- a UUID row, both now mapping to the same user_profile_id. Keep the newest.
+DELETE FROM user_preferences a
+  USING user_preferences b
+  WHERE a.user_profile_id = b.user_profile_id
+    AND a.user_profile_id IS NOT NULL
+    AND (a.updated_at < b.updated_at OR (a.updated_at = b.updated_at AND a.id < b.id));
+
 UPDATE saved_stations SET user_profile_id = up.id
   FROM user_profiles up WHERE saved_stations.user_id = up.auth0_sub AND saved_stations.user_profile_id IS NULL;