diff --git a/CHANGELOG.md b/CHANGELOG.md
index df9c47df9..fa56344c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,7 +42,7 @@ You should also include the user name that made the change.
 - Server: Bug fix for Pinned Users lookup on instance @squidicuzz
 - Server: Fix peers API returning suspended instances @ineffyble
 - Server: trim long text of note from ap @syuilo
-- Server: Ap inboxの最大ペイロードサイズを256kbに制限 @syuilo
+- Server: Ap inboxの最大ペイロードサイズを64kbに制限 @syuilo
 - Client: case insensitive emoji search @saschanaz
 - Client: InAppウィンドウが操作できなくなることがあるのを修正 @tamaina
 - Client: use proxied image for instance icon @syuilo
diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index d0df57121..bdd2e9750 100644
--- a/packages/backend/src/server/ActivityPubServerService.ts
+++ b/packages/backend/src/server/ActivityPubServerService.ts
@@ -438,9 +438,9 @@ export class ActivityPubServerService {
 		fastify.addContentTypeParser('application/ld+json', { parseAs: 'string' }, fastify.getDefaultJsonParser('ignore', 'ignore'));
 
 		//#region Routing
-		// inbox (limit: 256kb)
-		fastify.post('/inbox', { bodyLimit: 1024 * 256 }, async (request, reply) => await this.inbox(request, reply));
-		fastify.post('/users/:user/inbox', { bodyLimit: 1024 * 256 }, async (request, reply) => await this.inbox(request, reply));
+		// inbox (limit: 64kb)
+		fastify.post('/inbox', { bodyLimit: 1024 * 64 }, async (request, reply) => await this.inbox(request, reply));
+		fastify.post('/users/:user/inbox', { bodyLimit: 1024 * 64 }, async (request, reply) => await this.inbox(request, reply));
 
 		// note
 		fastify.get<{ Params: { note: string; } }>('/notes/:note', { constraints: { apOrHtml: 'ap' } }, async (request, reply) => {