diff --git a/backend/src/api/private/auth/auth.controller.ts b/backend/src/api/private/auth/auth.controller.ts
index 501d5a8a8..6dbdb9ade 100644
--- a/backend/src/api/private/auth/auth.controller.ts
+++ b/backend/src/api/private/auth/auth.controller.ts
@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
  *
  * SPDX-License-Identifier: AGPL-3.0-only
  */
@@ -53,7 +53,7 @@ export class AuthController {
 
   @UseGuards(RegistrationEnabledGuard)
   @Post('local')
-  @OpenApi(201, 400, 409)
+  @OpenApi(201, 400, 403, 409)
   async registerUser(
     @Req() request: RequestWithSession,
     @Body() registerDto: RegisterDto,
diff --git a/backend/src/api/utils/registration-enabled.guard.ts b/backend/src/api/utils/registration-enabled.guard.ts
index 6289f857f..8d4cce503 100644
--- a/backend/src/api/utils/registration-enabled.guard.ts
+++ b/backend/src/api/utils/registration-enabled.guard.ts
@@ -1,16 +1,12 @@
 /*
- * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
  *
  * SPDX-License-Identifier: AGPL-3.0-only
  */
-import {
-  BadRequestException,
-  CanActivate,
-  Inject,
-  Injectable,
-} from '@nestjs/common';
+import { CanActivate, Inject, Injectable } from '@nestjs/common';
 
 import authConfiguration, { AuthConfig } from '../../config/auth.config';
+import { RegistrationDisabledError } from '../../errors/errors';
 import { ConsoleLoggerService } from '../../logger/console-logger.service';
 
 @Injectable()
@@ -26,7 +22,7 @@ export class RegistrationEnabledGuard implements CanActivate {
   canActivate(): boolean {
     if (!this.authConfig.local.enableRegister) {
       this.logger.debug('User registration is disabled.', 'canActivate');
-      throw new BadRequestException('User registration is disabled.');
+      throw new RegistrationDisabledError();
     }
     return true;
   }
diff --git a/backend/src/errors/error-mapping.ts b/backend/src/errors/error-mapping.ts
index 92de02444..0a31e1ff4 100644
--- a/backend/src/errors/error-mapping.ts
+++ b/backend/src/errors/error-mapping.ts
@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
  *
  * SPDX-License-Identifier: AGPL-3.0-only
  */
@@ -8,6 +8,7 @@ import {
   BadRequestException,
   Catch,
   ConflictException,
+  ForbiddenException,
   InternalServerErrorException,
   NotFoundException,
   PayloadTooLargeException,
@@ -75,6 +76,10 @@ const mapOfHedgeDocErrorsToHttpErrors: Map<string, HttpExceptionConstructor> =
       'MaximumDocumentLengthExceededError',
       (object): HttpException => new PayloadTooLargeException(object),
     ],
+    [
+      'RegistrationDisabledError',
+      (object): HttpException => new ForbiddenException(object),
+    ],
   ]);
 
 @Catch()
diff --git a/backend/src/errors/errors.ts b/backend/src/errors/errors.ts
index edfe0936f..4010d420f 100644
--- a/backend/src/errors/errors.ts
+++ b/backend/src/errors/errors.ts
@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
  *
  * SPDX-License-Identifier: AGPL-3.0-only
  */
@@ -59,3 +59,7 @@ export class PasswordTooWeakError extends Error {
 export class MaximumDocumentLengthExceededError extends Error {
   name = 'MaximumDocumentLengthExceededError';
 }
+
+export class RegistrationDisabledError extends Error {
+  name = 'RegistrationDisabledError';
+}