diff --git a/packages/backend/src/server/api/endpoints/meta.ts b/packages/backend/src/server/api/endpoints/meta.ts
index 584ea07c3..53d724a9d 100644
--- a/packages/backend/src/server/api/endpoints/meta.ts
+++ b/packages/backend/src/server/api/endpoints/meta.ts
@@ -1,5 +1,6 @@
 import { IsNull, LessThanOrEqual, MoreThan } from 'typeorm';
 import { Inject, Injectable } from '@nestjs/common';
+import * as JSON5 from 'json5';
 import type { AdsRepository, UsersRepository } from '@/models/index.js';
 import { MAX_NOTE_TEXT_LENGTH } from '@/const.js';
 import { Endpoint } from '@/server/api/endpoint-base.js';
@@ -292,8 +293,9 @@ export default class extends Endpoint<typeof meta, typeof paramDef> {
 				backgroundImageUrl: instance.backgroundImageUrl,
 				logoImageUrl: instance.logoImageUrl,
 				maxNoteTextLength: MAX_NOTE_TEXT_LENGTH,
-				defaultLightTheme: instance.defaultLightTheme,
-				defaultDarkTheme: instance.defaultDarkTheme,
+				// クライアントの手間を減らすためあらかじめJSONに変換しておく
+				defaultLightTheme: instance.defaultLightTheme ? JSON.stringify(JSON5.parse(instance.defaultLightTheme)) : null,
+				defaultDarkTheme: instance.defaultDarkTheme ? JSON.stringify(JSON5.parse(instance.defaultDarkTheme)) : null,
 				ads: ads.map(ad => ({
 					id: ad.id,
 					url: ad.url,
diff --git a/packages/frontend/src/boot/common.ts b/packages/frontend/src/boot/common.ts
index e9d6586f8..e1b12fe7d 100644
--- a/packages/frontend/src/boot/common.ts
+++ b/packages/frontend/src/boot/common.ts
@@ -1,6 +1,5 @@
 import { computed, createApp, watch, markRaw, version as vueVersion, defineAsyncComponent, App } from 'vue';
 import { compareVersions } from 'compare-versions';
-import JSON5 from 'json5';
 import widgets from '@/widgets';
 import directives from '@/directives';
 import components from '@/components';
@@ -180,8 +179,8 @@ export async function common(createVue: () => App<Element>) {
 
 	fetchInstanceMetaPromise.then(() => {
 		if (defaultStore.state.themeInitial) {
-			if (instance.defaultLightTheme != null) ColdDeviceStorage.set('lightTheme', JSON5.parse(instance.defaultLightTheme));
-			if (instance.defaultDarkTheme != null) ColdDeviceStorage.set('darkTheme', JSON5.parse(instance.defaultDarkTheme));
+			if (instance.defaultLightTheme != null) ColdDeviceStorage.set('lightTheme', JSON.parse(instance.defaultLightTheme));
+			if (instance.defaultDarkTheme != null) ColdDeviceStorage.set('darkTheme', JSON.parse(instance.defaultDarkTheme));
 			defaultStore.set('themeInitial', false);
 		}
 	});
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 4a1219a74..711e0dc0a 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -5535,7 +5535,7 @@ packages:
       ts-dedent: 2.2.0
       util-deprecate: 1.0.2
       watchpack: 2.4.0
-      ws: 8.13.0
+      ws: 8.13.0(bufferutil@4.0.7)(utf-8-validate@6.0.3)
     transitivePeerDependencies:
       - bufferutil
       - encoding
@@ -8702,7 +8702,6 @@ packages:
     requiresBuild: true
     dependencies:
       node-gyp-build: 4.6.0
-    dev: false
 
   /bullmq@3.14.1:
     resolution: {integrity: sha512-Fom78UKljYsnJmwbROVPx3eFLuVfQjQbw9KCnVupLzT31RQHhFHV2xd/4J4oWl4u34bZ1JmEUfNnqNBz+IOJuA==}
@@ -15259,7 +15258,6 @@ packages:
   /node-gyp-build@4.6.0:
     resolution: {integrity: sha512-NTZVKn9IylLwUzaKjkas1e4u2DLNcV4rdYagA4PWdPwW87Bi7z+BznyKSRwS/761tV/lzCGXplWsiaMjLqP2zQ==}
     hasBin: true
-    dev: false
 
   /node-gyp@9.3.1:
     resolution: {integrity: sha512-4Q16ZCqq3g8awk6UplT7AuxQ35XN4R/yf/+wSAwcBUAjg7l58RTactWaP8fIDTi0FzI7YcVLujwExakZlfWkXg==}
@@ -19676,7 +19674,6 @@ packages:
     requiresBuild: true
     dependencies:
       node-gyp-build: 4.6.0
-    dev: false
 
   /util-deprecate@1.0.2:
     resolution: {integrity: sha512-EPD5q1uXyFxJpCrLnCc1nHnq3gOa6DZBocAIiI2TaSCA7VCJ1UJDMagCzIkXNsUYfD1daK//LTEQ8xiIbrHtcw==}
@@ -20326,19 +20323,6 @@ packages:
       async-limiter: 1.0.1
     dev: true
 
-  /ws@8.13.0:
-    resolution: {integrity: sha512-x9vcZYTrFPC7aSIbj7sRCYo7L/Xb8Iy+pW0ng0wt2vCJv7M9HOMy0UoN3rr+IFC7hb7vXoqS+P9ktyLLLhO+LA==}
-    engines: {node: '>=10.0.0'}
-    peerDependencies:
-      bufferutil: ^4.0.1
-      utf-8-validate: '>=5.0.2'
-    peerDependenciesMeta:
-      bufferutil:
-        optional: true
-      utf-8-validate:
-        optional: true
-    dev: true
-
   /ws@8.13.0(bufferutil@4.0.7)(utf-8-validate@6.0.3):
     resolution: {integrity: sha512-x9vcZYTrFPC7aSIbj7sRCYo7L/Xb8Iy+pW0ng0wt2vCJv7M9HOMy0UoN3rr+IFC7hb7vXoqS+P9ktyLLLhO+LA==}
     engines: {node: '>=10.0.0'}
@@ -20353,7 +20337,6 @@ packages:
     dependencies:
       bufferutil: 4.0.7
       utf-8-validate: 6.0.3
-    dev: false
 
   /xev@3.0.2:
     resolution: {integrity: sha512-8kxuH95iMXzHZj+fwqfA4UrPcYOy6bGIgfWzo9Ji23JoEc30ge/Z++Ubkiuy8c0+M64nXmmxrmJ7C8wnuBhluw==}