diff --git a/src/rollup/index.ts b/src/rollup/index.ts
index 4b6f2024..5d9b5f89 100644
--- a/src/rollup/index.ts
+++ b/src/rollup/index.ts
@@ -1,17 +1,17 @@
 import type { RollupPlugin, UnpluginContextMeta, UnpluginFactory, UnpluginInstance, UnpluginOptions } from '../types'
 import { toArray } from '../utils'
 
-export function getRollupPlugin <UserOptions = {}>(
-  factory: UnpluginFactory<UserOptions>,
-): UnpluginInstance<UserOptions>['rollup'] {
-  return (userOptions?: UserOptions) => {
+export function getRollupPlugin <UserOptions = {}, Nested extends boolean = boolean>(
+  factory: UnpluginFactory<UserOptions, Nested>,
+) {
+  return ((userOptions?: UserOptions) => {
     const meta: UnpluginContextMeta = {
       framework: 'rollup',
     }
     const rawPlugins = toArray(factory(userOptions!, meta))
     const plugins = rawPlugins.map(plugin => toRollupPlugin(plugin))
     return plugins.length === 1 ? plugins[0] : plugins
-  }
+  }) as UnpluginInstance<UserOptions, Nested>['rollup']
 }
 
 export function toRollupPlugin(plugin: UnpluginOptions, containRollupOptions = true): RollupPlugin {
diff --git a/src/types.ts b/src/types.ts
index 2322bac8..3fcd1ee5 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -69,7 +69,7 @@ export interface ResolvedUnpluginOptions extends UnpluginOptions {
   __virtualModulePrefix: string
 }
 
-export type UnpluginFactory<UserOptions, Nested extends boolean> = (options: UserOptions, meta: UnpluginContextMeta) =>
+export type UnpluginFactory<UserOptions, Nested extends boolean = boolean> = (options: UserOptions, meta: UnpluginContextMeta) =>
 Nested extends true
   ? Array<UnpluginOptions>
   : UnpluginOptions
@@ -77,7 +77,7 @@ export type UnpluginFactoryOutput<UserOptions, Return> = undefined extends UserO
   ? (options?: UserOptions) => Return
   : (options: UserOptions) => Return
 
-export interface UnpluginInstance<UserOptions, Nested extends boolean> {
+export interface UnpluginInstance<UserOptions, Nested extends boolean = boolean> {
   rollup: UnpluginFactoryOutput<UserOptions, Nested extends true ? Array<RollupPlugin> : RollupPlugin>
   vite: UnpluginFactoryOutput<UserOptions, Nested extends true ? Array<VitePlugin> : VitePlugin>
   webpack: UnpluginFactoryOutput<UserOptions, WebpackPluginInstance>
diff --git a/src/vite/index.ts b/src/vite/index.ts
index f9eec52f..2a1824ad 100644
--- a/src/vite/index.ts
+++ b/src/vite/index.ts
@@ -2,10 +2,10 @@ import { toRollupPlugin } from '../rollup'
 import type { UnpluginContextMeta, UnpluginFactory, UnpluginInstance, VitePlugin } from '../types'
 import { toArray } from '../utils'
 
-export function getVitePlugin <UserOptions = {}>(
-  factory: UnpluginFactory<UserOptions>,
-): UnpluginInstance<UserOptions>['vite'] {
-  return (userOptions?: UserOptions) => {
+export function getVitePlugin <UserOptions = {}, Nested extends boolean = boolean>(
+  factory: UnpluginFactory<UserOptions, Nested>,
+) {
+  return ((userOptions?: UserOptions) => {
     const meta: UnpluginContextMeta = {
       framework: 'vite',
     }
@@ -20,5 +20,5 @@ export function getVitePlugin <UserOptions = {}>(
     })
 
     return plugins.length === 1 ? plugins[0] : plugins
-  }
+  }) as UnpluginInstance<UserOptions, Nested>['vite']
 }