diff --git a/packages/backend/migration/1750591589187-registry-unique-constraints.js b/packages/backend/migration/1750591589187-registry-unique-constraints.js
new file mode 100644
index 0000000000..e9fa6f609d
--- /dev/null
+++ b/packages/backend/migration/1750591589187-registry-unique-constraints.js
@@ -0,0 +1,19 @@
+/*
+ * SPDX-FileCopyrightText: dakkar and other Sharkey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class RegistryUniqueConstraints1750591589187 {
+	async up(queryRunner) {
+		await queryRunner.query(`DELETE FROM "registry_item" WHERE "id" IN (
+SELECT t."id" FROM (
+SELECT *, ROW_NUMBER() OVER (PARTITION BY "userId","key","scope","domain" ORDER BY "updatedAt" DESC) rn
+FROM "registry_item"
+) t WHERE t.rn>1)`);
+		await queryRunner.query(`CREATE UNIQUE INDEX "IDX_d9c48d580287308f8c1f674946" ON "registry_item" ("userId", "key", "scope", "domain") NULLS NOT DISTINCT`);
+	}
+
+	async down(queryRunner) {
+		await queryRunner.query(`DROP INDEX "public"."IDX_d9c48d580287308f8c1f674946"`);
+	}
+}
diff --git a/packages/backend/src/core/RegistryApiService.ts b/packages/backend/src/core/RegistryApiService.ts
index 2c8877d8a8..2c7ad4026d 100644
--- a/packages/backend/src/core/RegistryApiService.ts
+++ b/packages/backend/src/core/RegistryApiService.ts
@@ -27,25 +27,9 @@ export class RegistryApiService {
 	public async set(userId: MiUser['id'], domain: string | null, scope: string[], key: string, value: any) {
 		// TODO: 作成できるキーの数を制限する
 
-		const query = this.registryItemsRepository.createQueryBuilder('item');
-		if (domain) {
-			query.where('item.domain = :domain', { domain: domain });
-		} else {
-			query.where('item.domain IS NULL');
-		}
-		query.andWhere('item.userId = :userId', { userId: userId });
-		query.andWhere('item.key = :key', { key: key });
-		query.andWhere('item.scope = :scope', { scope: scope });
-
-		const existingItem = await query.getOne();
-
-		if (existingItem) {
-			await this.registryItemsRepository.update(existingItem.id, {
-				updatedAt: new Date(),
-				value: value,
-			});
-		} else {
-			await this.registryItemsRepository.insert({
+		await this.registryItemsRepository.createQueryBuilder('item')
+			.insert()
+			.values({
 				id: this.idService.gen(),
 				updatedAt: new Date(),
 				userId: userId,
@@ -53,8 +37,13 @@ export class RegistryApiService {
 				scope: scope,
 				key: key,
 				value: value,
-			});
-		}
+			})
+			.orUpdate(
+				['updatedAt', 'value'],
+				['userId', 'key', 'scope', 'domain'],
+				{ upsertType: 'on-conflict-do-update' }
+			)
+			.execute();
 
 		if (domain == null) {
 			// TODO: サードパーティアプリが傍受出来てしまうのでどうにかする
diff --git a/packages/backend/src/models/RegistryItem.ts b/packages/backend/src/models/RegistryItem.ts
index 335e8b9eab..ceb0305bb4 100644
--- a/packages/backend/src/models/RegistryItem.ts
+++ b/packages/backend/src/models/RegistryItem.ts
@@ -7,8 +7,8 @@ import { PrimaryColumn, Entity, Index, JoinColumn, Column, ManyToOne } from 'typ
 import { id } from './util/id.js';
 import { MiUser } from './User.js';
 
-// TODO: 同じdomain、同じscope、同じkeyのレコードは二つ以上存在しないように制約付けたい
 @Entity('registry_item')
+@Index(['userId', 'key', 'scope', 'domain'], { unique: true })
 export class MiRegistryItem {
 	@PrimaryColumn(id())
 	public id: string;