diff --git a/packages/backend/src/server/api/endpoints/meta.ts b/packages/backend/src/server/api/endpoints/meta.ts
index 139afc88ba..23cfe40184 100644
--- a/packages/backend/src/server/api/endpoints/meta.ts
+++ b/packages/backend/src/server/api/endpoints/meta.ts
@@ -1,3 +1,4 @@
+import * as JSON5 from "json5";
 import { IsNull, MoreThan } from "typeorm";
 import config from "@/config/index.js";
 import { fetchMeta } from "@/misc/fetch-meta.js";
@@ -462,8 +463,13 @@ export default define(meta, paramDef, async (ps, me) => {
 		maxNoteTextLength: MAX_NOTE_TEXT_LENGTH, // 後方互換性のため
 		maxCaptionTextLength: MAX_CAPTION_TEXT_LENGTH,
 		emojis: instance.privateMode && !me ? [] : await Emojis.packMany(emojis),
-		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:
 			instance.privateMode && !me
 				? []
diff --git a/packages/client/src/init.ts b/packages/client/src/init.ts
index 7a004688d6..5d9ae12f36 100644
--- a/packages/client/src/init.ts
+++ b/packages/client/src/init.ts
@@ -27,7 +27,6 @@ import {
 	defineAsyncComponent,
 } from "vue";
 import { compareVersions } from "compare-versions";
-import JSON5 from "json5";
 
 import widgets from "@/widgets";
 import directives from "@/directives";
@@ -312,12 +311,12 @@ import { getAccountFromId } from "@/scripts/get-account-from-id";
 			if (instance.defaultLightTheme != null)
 				ColdDeviceStorage.set(
 					"lightTheme",
-					JSON5.parse(instance.defaultLightTheme),
+					JSON.parse(instance.defaultLightTheme),
 				);
 			if (instance.defaultDarkTheme != null)
 				ColdDeviceStorage.set(
 					"darkTheme",
-					JSON5.parse(instance.defaultDarkTheme),
+					JSON.parse(instance.defaultDarkTheme),
 				);
 			defaultStore.set("themeInitial", false);
 		}