diff --git a/apps/edr-passenger-api/prisma/migrations/20260718144855_unique_constraint_schedule_id_seat_id_departure_station_id/migration.sql b/apps/edr-passenger-api/prisma/migrations/20260718144855_unique_constraint_schedule_id_seat_id_departure_station_id/migration.sql
index a512eeccd..d19281e3c 100644
--- a/apps/edr-passenger-api/prisma/migrations/20260718144855_unique_constraint_schedule_id_seat_id_departure_station_id/migration.sql
+++ b/apps/edr-passenger-api/prisma/migrations/20260718144855_unique_constraint_schedule_id_seat_id_departure_station_id/migration.sql
@@ -15,6 +15,7 @@ WHERE id NOT IN (
 )
 AND "seatId" IS NOT NULL;
 
--- CreateIndex
+-- CreateIndex (partial: only index rows where seatId is not null so NULL rows never collide)
 CREATE UNIQUE INDEX IF NOT EXISTS "JourneySegment_scheduleId_seatId_departureStationId_key"
-  ON "JourneySegment"("scheduleId", "seatId", "departureStationId");
+  ON passenger."JourneySegment"("scheduleId", "seatId", "departureStationId")
+  WHERE ("seatId" IS NOT NULL);