diff --git a/packages/backend/src/server/api/endpoint-base.ts b/packages/backend/src/server/api/endpoint-base.ts
index d5279faa1c..bae68c93dc 100644
--- a/packages/backend/src/server/api/endpoint-base.ts
+++ b/packages/backend/src/server/api/endpoint-base.ts
@@ -9,6 +9,7 @@ import type { Schema, SchemaType } from '@/misc/json-schema.js';
 import type { MiLocalUser } from '@/models/User.js';
 import type { MiAccessToken } from '@/models/AccessToken.js';
 import { ApiError } from './error.js';
+import { omitAjvNotSupportProperty } from './openapi/schemas.js';
 import type { IEndpointMeta } from './endpoints.js';
 
 const Ajv = _Ajv.default;
@@ -35,7 +36,8 @@ export abstract class Endpoint<T extends IEndpointMeta, Ps extends Schema> {
 	public exec: (params: any, user: T['requireCredential'] extends true ? MiLocalUser : MiLocalUser | null, token: MiAccessToken | null, file?: File, ip?: string | null, headers?: Record<string, string> | null) => Promise<any>;
 
 	constructor(meta: T, paramDef: Ps, cb: Executor<T, Ps>) {
-		const validate = ajv.compile(paramDef);
+		const ajvSchema = omitAjvNotSupportProperty(paramDef);
+		const validate = ajv.compile(ajvSchema);
 
 		this.exec = (params: any, user: T['requireCredential'] extends true ? MiLocalUser : MiLocalUser | null, token: MiAccessToken | null, file?: File, ip?: string | null, headers?: Record<string, string> | null) => {
 			let cleanup: undefined | (() => void) = undefined;
diff --git a/packages/backend/src/server/api/endpoints/federation/instances.ts b/packages/backend/src/server/api/endpoints/federation/instances.ts
index f6fb0c6de5..e5a90715f5 100644
--- a/packages/backend/src/server/api/endpoints/federation/instances.ts
+++ b/packages/backend/src/server/api/endpoints/federation/instances.ts
@@ -44,7 +44,7 @@ export const paramDef = {
 		offset: { type: 'integer', default: 0 },
 		sort: {
 			type: 'string',
-			optional: true, nullable: true,
+			nullable: true,
 			enum: [
 				'+pubSub',
 				'-pubSub',
diff --git a/packages/backend/src/server/api/openapi/schemas.ts b/packages/backend/src/server/api/openapi/schemas.ts
index 2716f5f162..e970b3f824 100644
--- a/packages/backend/src/server/api/openapi/schemas.ts
+++ b/packages/backend/src/server/api/openapi/schemas.ts
@@ -43,6 +43,19 @@ export function convertSchemaToOpenApiSchema(schema: Schema) {
 	return res;
 }
 
+export function omitAjvNotSupportProperty(schema: Schema): Schema {
+	// eslint-disable-next-line @typescript-eslint/no-unused-vars
+	const { optional, ref, ...res } = JSON.parse(JSON.stringify(schema)) as Schema;
+
+	if (res.type === 'object' && res.properties) {
+		for (const k of Object.keys(res.properties)) {
+			res.properties[k] = omitAjvNotSupportProperty(res.properties[k]);
+		}
+	}
+
+	return res;
+}
+
 export const schemas = {
 	Error: {
 		type: 'object',