diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad070cc981..6359033c1b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,7 @@
 -
 
 ### Client
--
+- サイズ制限を超過するファイルをアップロードしようとした際にエラーを出すように
 
 ### Server
 - ファイルがサイズの制限を超えてアップロードされた際にエラーを返さなかった問題を修正
diff --git a/packages/backend/src/config.ts b/packages/backend/src/config.ts
index 3e5a1e81cd..cff0194780 100644
--- a/packages/backend/src/config.ts
+++ b/packages/backend/src/config.ts
@@ -133,7 +133,7 @@ export type Config = {
 	proxySmtp: string | undefined;
 	proxyBypassHosts: string[] | undefined;
 	allowedPrivateNetworks: string[] | undefined;
-	maxFileSize: number | undefined;
+	maxFileSize: number;
 	clusterLimit: number | undefined;
 	id: string;
 	outgoingAddress: string | undefined;
@@ -250,7 +250,7 @@ export function loadConfig(): Config {
 		proxySmtp: config.proxySmtp,
 		proxyBypassHosts: config.proxyBypassHosts,
 		allowedPrivateNetworks: config.allowedPrivateNetworks,
-		maxFileSize: config.maxFileSize,
+		maxFileSize: config.maxFileSize ?? 262144000,
 		clusterLimit: config.clusterLimit,
 		outgoingAddress: config.outgoingAddress,
 		outgoingAddressFamily: config.outgoingAddressFamily,
diff --git a/packages/backend/src/core/DownloadService.ts b/packages/backend/src/core/DownloadService.ts
index 21ae798f9f..93f4a38246 100644
--- a/packages/backend/src/core/DownloadService.ts
+++ b/packages/backend/src/core/DownloadService.ts
@@ -42,7 +42,7 @@ export class DownloadService {
 
 		const timeout = 30 * 1000;
 		const operationTimeout = 60 * 1000;
-		const maxSize = this.config.maxFileSize ?? 262144000;
+		const maxSize = this.config.maxFileSize;
 
 		const urlObj = new URL(url);
 		let filename = urlObj.pathname.split('/').pop() ?? 'untitled';
diff --git a/packages/backend/src/core/entities/MetaEntityService.ts b/packages/backend/src/core/entities/MetaEntityService.ts
index 44ec0d6a7b..f4b1e302d0 100644
--- a/packages/backend/src/core/entities/MetaEntityService.ts
+++ b/packages/backend/src/core/entities/MetaEntityService.ts
@@ -129,6 +129,7 @@ export class MetaEntityService {
 			mediaProxy: this.config.mediaProxy,
 			enableUrlPreview: instance.urlPreviewEnabled,
 			noteSearchableScope: (this.config.meilisearch == null || this.config.meilisearch.scope !== 'local') ? 'global' : 'local',
+			maxFileSize: this.config.maxFileSize,
 		};
 
 		return packed;
diff --git a/packages/backend/src/models/json-schema/meta.ts b/packages/backend/src/models/json-schema/meta.ts
index 3bcf9cac92..99feeaa7d7 100644
--- a/packages/backend/src/models/json-schema/meta.ts
+++ b/packages/backend/src/models/json-schema/meta.ts
@@ -253,6 +253,10 @@ export const packedMetaLiteSchema = {
 			optional: false, nullable: false,
 			default: 'local',
 		},
+		maxFileSize: {
+			type: 'number',
+			optional: false, nullable: false,
+		},
 	},
 } as const;
 
diff --git a/packages/backend/src/server/api/ApiServerService.ts b/packages/backend/src/server/api/ApiServerService.ts
index 4a5935f930..13cbdfc3be 100644
--- a/packages/backend/src/server/api/ApiServerService.ts
+++ b/packages/backend/src/server/api/ApiServerService.ts
@@ -49,7 +49,7 @@ export class ApiServerService {
 
 		fastify.register(multipart, {
 			limits: {
-				fileSize: this.config.maxFileSize ?? 262144000,
+				fileSize: this.config.maxFileSize,
 				files: 1,
 			},
 		});
diff --git a/packages/frontend/src/scripts/upload.ts b/packages/frontend/src/scripts/upload.ts
index 3e947183c9..abb0e1e677 100644
--- a/packages/frontend/src/scripts/upload.ts
+++ b/packages/frontend/src/scripts/upload.ts
@@ -13,6 +13,7 @@ import { apiUrl } from '@/config.js';
 import { $i } from '@/account.js';
 import { alert } from '@/os.js';
 import { i18n } from '@/i18n.js';
+import { instance } from '@/instance.js';
 
 type Uploading = {
 	id: string;
@@ -39,6 +40,15 @@ export function uploadFile(
 
 	if (folder && typeof folder === 'object') folder = folder.id;
 
+	if (file.size > instance.maxFileSize) {
+		alert({
+			type: 'error',
+			title: i18n.ts.failedToUpload,
+			text: i18n.ts.cannotUploadBecauseExceedsFileSizeLimit,
+		});
+		return Promise.reject();
+	}
+
 	return new Promise((resolve, reject) => {
 		const id = uuid();
 
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 6d2f787767..0c50825203 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -4947,6 +4947,7 @@ export type components = {
        * @enum {string}
        */
       noteSearchableScope: 'local' | 'global';
+      maxFileSize: number;
     };
     MetaDetailedOnly: {
       features?: {