diff --git a/packages/backend/src/server/api/index.ts b/packages/backend/src/server/api/index.ts
index e2a0257e61..f1889a8b67 100644
--- a/packages/backend/src/server/api/index.ts
+++ b/packages/backend/src/server/api/index.ts
@@ -60,7 +60,7 @@ router.use(
 	}),
 );
 
-mastoRouter.use(koaBody());
+mastoRouter.use(koaBody({ multipart: true }));
 
 apiMastodonCompatible(mastoRouter);
 
diff --git a/packages/backend/src/server/index.ts b/packages/backend/src/server/index.ts
index a3cdad4387..521f3ddf6e 100644
--- a/packages/backend/src/server/index.ts
+++ b/packages/backend/src/server/index.ts
@@ -72,7 +72,7 @@ app.use(mount("/proxy", proxyServer));
 const router = new Router();
 const mastoRouter = new Router();
 
-mastoRouter.use(koaBody());
+mastoRouter.use(koaBody({ multipart: true }));
 
 // Routing
 router.use(activityPub.routes());