diff --git a/backend/services/mpc-service/prisma/schema.prisma b/backend/services/mpc-service/prisma/schema.prisma
index 7570d6e3..ee5f95aa 100644
--- a/backend/services/mpc-service/prisma/schema.prisma
+++ b/backend/services/mpc-service/prisma/schema.prisma
@@ -38,14 +38,13 @@ model MpcWallet {
 // =============================================================================
 model MpcShare {
   id             String   @id @default(uuid())
-  username       String   @db.VarChar(255)
+  username       String   @unique @db.VarChar(255)
   partyId        String   @map("party_id") @db.VarChar(255)
   partyIndex     Int      @map("party_index")
   encryptedShare String   @map("encrypted_share") @db.Text
   createdAt      DateTime @default(now()) @map("created_at")
   updatedAt      DateTime @updatedAt @map("updated_at")
 
-  @@unique([username], name: "uq_ms_username")
   @@index([username], name: "idx_ms_username")
   @@map("mpc_shares")
 }