diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index a4ac2375c0..27d25d2152 100644
--- a/packages/backend/src/server/ActivityPubServerService.ts
+++ b/packages/backend/src/server/ActivityPubServerService.ts
@@ -33,7 +33,7 @@ import type Logger from '@/logger.js';
 import { LoggerService } from '@/core/LoggerService.js';
 import { bindThis } from '@/decorators.js';
 import { IActivity, IAnnounce, ICreate } from '@/core/activitypub/type.js';
-import { isQuote, isRenote } from '@/misc/is-renote.js';
+import { isPureRenote, isQuote, isRenote } from '@/misc/is-renote.js';
 import * as Acct from '@/misc/acct.js';
 import { CacheService } from '@/core/CacheService.js';
 import type { FastifyInstance, FastifyRequest, FastifyReply, FastifyPluginOptions, FastifyBodyParser } from 'fastify';
@@ -842,6 +842,11 @@ export class ActivityPubServerService {
 				return;
 			}
 
+			// Boosts don't federate directly - they should only be referenced as an activity
+			if (isPureRenote(note)) {
+				return 404;
+			}
+
 			this.setResponseType(request, reply);
 
 			const author = await this.usersRepository.findOneByOrFail({ id: note.userId });