diff --git a/packages/backend/src/core/UserCacheService.ts b/packages/backend/src/core/UserCacheService.ts
index 3f735c0c5..4d9ee7366 100644
--- a/packages/backend/src/core/UserCacheService.ts
+++ b/packages/backend/src/core/UserCacheService.ts
@@ -2,7 +2,7 @@ import { Inject, Injectable } from '@nestjs/common';
 import Redis from 'ioredis';
 import type { UsersRepository } from '@/models/index.js';
 import { Cache } from '@/misc/cache.js';
-import type { CacheableLocalUser, CacheableUser, ILocalUser } from '@/models/entities/User.js';
+import type { CacheableLocalUser, CacheableUser, ILocalUser, User } from '@/models/entities/User.js';
 import { DI } from '@/di-symbols.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { bindThis } from '@/decorators.js';
@@ -68,6 +68,11 @@ export class UserCacheService implements OnApplicationShutdown {
 		}
 	}
 
+	@bindThis
+	public findById(userId: User['id']) {
+		return this.userByIdCache.fetch(userId, () => this.usersRepository.findOneByOrFail({ id: userId }));
+	}
+
 	@bindThis
 	public onApplicationShutdown(signal?: string | undefined) {
 		this.redisSubscriber.off('message', this.onMessage);
diff --git a/packages/backend/src/core/activitypub/ApDbResolverService.ts b/packages/backend/src/core/activitypub/ApDbResolverService.ts
index 1f28fb3a0..1d0c2d5da 100644
--- a/packages/backend/src/core/activitypub/ApDbResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApDbResolverService.ts
@@ -159,7 +159,7 @@ export class ApDbResolverService {
 		if (key == null) return null;
 
 		return {
-			user: await this.userCacheService.userByIdCache.fetch(key.userId, () => this.usersRepository.findOneByOrFail({ id: key.userId })) as CacheableRemoteUser,
+			user: await this.userCacheService.findById(key.userId) as CacheableRemoteUser,
 			key,
 		};
 	}