diff --git a/packages/backend/src/error.ts b/packages/backend/src/error.ts
deleted file mode 100644
index b906147627..0000000000
--- a/packages/backend/src/error.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-/*
- * SPDX-FileCopyrightText: tamaina and other misskey contributors
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-// Never use `./error.js` because jest can't use it.
diff --git a/packages/backend/src/misc/error.ts b/packages/backend/src/misc/error.ts
index 2ea56dd96c..57df15c30b 100644
--- a/packages/backend/src/misc/error.ts
+++ b/packages/backend/src/misc/error.ts
@@ -4,17 +4,10 @@
  */
 import { FastifyReply, FastifyRequest } from 'fastify';
 
-export function ErrorHandling(message: string, reply?: FastifyReply, statusCode?: number): Error {
-	const error = new Error(message);
+export async function ErrorHandler(error: Error, request: FastifyRequest, reply: FastifyReply): Promise<void> {
 	if (process.env.NODE_ENV === 'production') {
 		error.stack = undefined;
 	}
-	if (reply) {
-		reply.code(statusCode ?? 500);
-	}
-	return error;
-}
-
-export function ErrorHandler(error: Error, request: FastifyRequest, reply: FastifyReply): void {
-	throw ErrorHandling(error.message, reply);
+	reply.send(error);
+	throw error;
 }
diff --git a/packages/backend/src/misc/fastify-reply-error.ts b/packages/backend/src/misc/fastify-reply-error.ts
index 7f18cec8d5..8edfa87bdc 100644
--- a/packages/backend/src/misc/fastify-reply-error.ts
+++ b/packages/backend/src/misc/fastify-reply-error.ts
@@ -14,7 +14,7 @@ export class FastifyReplyError extends Error {
 		this.statusCode = statusCode;
 
 		if (process.env.NODE_ENV === 'production') {
-			Object.defineProperty(this, 'stack', { value: '' });
+			Object.defineProperty(this, 'stack', { value: undefined });
 		}
 	}
 }
diff --git a/packages/backend/src/server/oauth/OAuth2ProviderService.ts b/packages/backend/src/server/oauth/OAuth2ProviderService.ts
index 9eedded830..61c89a4258 100644
--- a/packages/backend/src/server/oauth/OAuth2ProviderService.ts
+++ b/packages/backend/src/server/oauth/OAuth2ProviderService.ts
@@ -353,7 +353,6 @@ export class OAuth2ProviderService {
 	public async createServer(fastify: FastifyInstance): Promise<void> {
 		// https://datatracker.ietf.org/doc/html/rfc8414.html
 		// https://indieauth.spec.indieweb.org/#indieauth-server-metadata
-
 		fastify.get('/.well-known/oauth-authorization-server', async (_request, reply) => {
 			reply.send({
 				issuer: this.config.url,