diff --git a/packages/backend/src/misc/prelude/maybe.ts b/packages/backend/src/misc/prelude/maybe.ts
deleted file mode 100644
index 1c58ccb9c..000000000
--- a/packages/backend/src/misc/prelude/maybe.ts
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-export interface IMaybe<T> {
-	isJust(): this is IJust<T>;
-}
-
-export interface IJust<T> extends IMaybe<T> {
-	get(): T;
-}
-
-export function just<T>(value: T): IJust<T> {
-	return {
-		isJust: () => true,
-		get: () => value,
-	};
-}
-
-export function nothing<T>(): IMaybe<T> {
-	return {
-		isJust: () => false,
-	};
-}
diff --git a/packages/backend/test/prelude/maybe.ts b/packages/backend/test/prelude/maybe.ts
deleted file mode 100644
index 16e92216d..000000000
--- a/packages/backend/test/prelude/maybe.ts
+++ /dev/null
@@ -1,23 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-import * as assert from 'assert';
-import { just, nothing } from '../../src/misc/prelude/maybe.js';
-
-describe('just', () => {
-	test('has a value', () => {
-		assert.deepStrictEqual(just(3).isJust(), true);
-	});
-
-	test('has the inverse called get', () => {
-		assert.deepStrictEqual(just(3).get(), 3);
-	});
-});
-
-describe('nothing', () => {
-	test('has no value', () => {
-		assert.deepStrictEqual(nothing().isJust(), false);
-	});
-});