diff --git a/docs/guide/configuration.md b/docs/guide/configuration.md
index 4ec74081..8ffaad52 100644
--- a/docs/guide/configuration.md
+++ b/docs/guide/configuration.md
@@ -24,7 +24,6 @@ module.exports = {
 
 Check out the [Config Reference](/config/basics) for a full list of options.
 
-
 ## Config Intellisense
 
 Since VitePress ships with TypeScript typings, you can leverage your IDE's intellisense with jsdoc type hints:
@@ -52,30 +51,29 @@ export default defineConfig({
 
 VitePress also directly supports TS config files. You can use `.vitepress/config.ts` with the `defineConfig` helper as well.
 
-
 ## Typed Theme Config
 
 By default, `defineConfig` helper leverages the theme config type from default theme:
 
-```js
+```ts
 import { defineConfig } from 'vitepress'
 
 export default defineConfig({
   themeConfig: {
-     // Type is `DefaultTheme.Config` 
+    // Type is `DefaultTheme.Config`
   }
 })
 ```
 
-If you use a custom theme, you'll be able to pass the generics type for your custom theme, and you need overload it with the second parameter of `defineConfig` helper:
+If you use a custom theme and want type checks for the theme config, you'll need to use `defineConfigWithTheme` instead, and pass the config type for your custom theme via a generic argument:
 
-```js
-import { defineConfig } from 'vitepress'
+```ts
+import { defineConfigWithTheme } from 'vitepress'
 import { ThemeConfig } from 'your-theme'
 
-export default defineConfig<ThemeConfig>({
+export default defineConfigWithTheme<ThemeConfig>({
   themeConfig: {
-    // Type is `ThemeConfig` 
+    // Type is `ThemeConfig`
   }
-}, true); // declare `usingCustomTheme` and discard usage of the default theme.
+})
 ```
diff --git a/src/node/config.ts b/src/node/config.ts
index 3c82976c..15ceaf72 100644
--- a/src/node/config.ts
+++ b/src/node/config.ts
@@ -15,7 +15,7 @@ import {
   HeadConfig,
   LocaleConfig,
   createLangDictionary,
-  DefaultTheme,
+  DefaultTheme
 } from './shared'
 import { resolveAliases, APP_PATH, DEFAULT_THEME_PATH } from './alias'
 import { MarkdownOptions } from './markdown/markdown'
@@ -27,16 +27,14 @@ const debug = _debug('vitepress:config')
 
 export type { MarkdownOptions }
 
-export type ThemeConfig = any;
-
-export interface UserConfig<T extends ThemeConfig = ThemeConfig> {
-  extends?: RawConfigExports<T>
+export interface UserConfig<ThemeConfig = any> {
+  extends?: RawConfigExports<ThemeConfig>
   lang?: string
   base?: string
   title?: string
   description?: string
   head?: HeadConfig[]
-  themeConfig?: T
+  themeConfig?: ThemeConfig
   locales?: Record<string, LocaleConfig>
   markdown?: MarkdownOptions
   /**
@@ -58,15 +56,15 @@ export interface UserConfig<T extends ThemeConfig = ThemeConfig> {
   mpa?: boolean
 }
 
-export type RawConfigExports<T extends ThemeConfig = ThemeConfig> =
-  | UserConfig<T>
-  | Promise<UserConfig<T>>
-  | (() => UserConfig<T> | Promise<UserConfig<T>>)
+export type RawConfigExports<ThemeConfig = any> =
+  | UserConfig<ThemeConfig>
+  | Promise<UserConfig<ThemeConfig>>
+  | (() => UserConfig<ThemeConfig> | Promise<UserConfig<ThemeConfig>>)
 
-export interface SiteConfig<T = ThemeConfig> {
+export interface SiteConfig<ThemeConfig = any> {
   root: string
   srcDir: string
-  site: SiteData<T>
+  site: SiteData<ThemeConfig>
   configPath: string | undefined
   themeDir: string
   outDir: string
@@ -85,12 +83,16 @@ const resolve = (root: string, file: string) =>
 /**
  * Type config helper
  */
- export function defineConfig<T extends ThemeConfig = ThemeConfig>(
-  config: UserConfig<T>,
-  usingCustomTheme: true
-): void
-export function defineConfig(config: UserConfig<DefaultTheme.Config>): void
-export function defineConfig(config: ThemeConfig) {
+export function defineConfig(config: UserConfig<DefaultTheme.Config>) {
+  return config
+}
+
+/**
+ * Type config helper for custom theme config
+ */
+export function defineConfigWithTheme<ThemeConfig>(
+  config: UserConfig<ThemeConfig>
+) {
   return config
 }
 
@@ -158,7 +160,7 @@ async function resolveUserConfig(
     }
   }
 
-  const userConfig: RawConfigExports<ThemeConfig> = configPath
+  const userConfig: RawConfigExports = configPath
     ? ((
         await loadConfigFromFile(
           {
@@ -181,7 +183,7 @@ async function resolveUserConfig(
 }
 
 async function resolveConfigExtends(
-  config: RawConfigExports<ThemeConfig>
+  config: RawConfigExports
 ): Promise<UserConfig> {
   const resolved = await (typeof config === 'function' ? config() : config)
   if (resolved.extends) {
diff --git a/types/shared.d.ts b/types/shared.d.ts
index 63fbb624..2beaf53f 100644
--- a/types/shared.d.ts
+++ b/types/shared.d.ts
@@ -11,7 +11,7 @@ export interface LocaleConfig {
   selectText?: string
 }
 
-export interface SiteData<T = any> {
+export interface SiteData<ThemeConfig = any> {
   base: string
   /**
    * Language of the site as it should be set on the `html` element.
@@ -21,7 +21,7 @@ export interface SiteData<T = any> {
   title: string
   description: string
   head: HeadConfig[]
-  themeConfig: T
+  themeConfig: ThemeConfig
   locales: Record<string, LocaleConfig>
   /**
    * Available locales for the site when it has defined `locales` in its