diff --git a/packages/client/src/pages/settings/theme.vue b/packages/client/src/pages/settings/theme.vue
index 92a6fee7a..d134a092b 100644
--- a/packages/client/src/pages/settings/theme.vue
+++ b/packages/client/src/pages/settings/theme.vue
@@ -101,7 +101,7 @@ import { ColdDeviceStorage } from '@/store';
 import { i18n } from '@/i18n';
 import { defaultStore } from '@/store';
 import { instance } from '@/instance';
-import { concat } from '@/scripts/array';
+import { concat, uniqueBy } from '@/scripts/array';
 import { fetchThemes, getThemes } from '@/theme-store';
 import * as symbols from '@/symbols';
 
@@ -128,7 +128,7 @@ export default defineComponent({
 		const instanceThemes = [];
 		if (instance.defaultLightTheme != null) instanceThemes.push(JSON5.parse(instance.defaultLightTheme));
 		if (instance.defaultDarkTheme != null) instanceThemes.push(JSON5.parse(instance.defaultDarkTheme));
-		const themes = computed(() => instanceThemes.concat(builtinThemes.concat(installedThemes.value)));
+		const themes = computed(() => uniqueBy(instanceThemes.concat(builtinThemes.concat(installedThemes.value)), theme => theme.id));
 		const darkThemes = computed(() => themes.value.filter(t => t.base === 'dark' || t.kind === 'dark'));
 		const lightThemes = computed(() => themes.value.filter(t => t.base === 'light' || t.kind === 'light'));
 		const darkTheme = ColdDeviceStorage.ref('darkTheme');
diff --git a/packages/client/src/scripts/array.ts b/packages/client/src/scripts/array.ts
index d63f0475d..29d027de1 100644
--- a/packages/client/src/scripts/array.ts
+++ b/packages/client/src/scripts/array.ts
@@ -52,6 +52,17 @@ export function unique<T>(xs: T[]): T[] {
 	return [...new Set(xs)];
 }
 
+export function uniqueBy<TValue, TKey>(values: TValue[], keySelector: (value: TValue) => TKey): TValue[] {
+	const map = new Map<TKey, TValue>();
+
+	for (const value of values) {
+		const key = keySelector(value);
+		if (!map.has(key)) map.set(key, value);
+	}
+
+	return [...map.values()];
+}
+
 export function sum(xs: number[]): number {
 	return xs.reduce((a, b) => a + b, 0);
 }