diff --git a/docs/advanced-features/custom-error-page.md b/docs/advanced-features/custom-error-page.md
index e3f4b2ddf79d..6b3a2b860b1b 100644
--- a/docs/advanced-features/custom-error-page.md
+++ b/docs/advanced-features/custom-error-page.md
@@ -98,3 +98,4 @@ If you have a custom `Error` component be sure to import that one instead. `next
 ### Caveats
 
 - `Error` does not currently support Next.js [Data Fetching methods](/docs/basic-features/data-fetching.md) like [`getStaticProps`](/docs/basic-features/data-fetching/get-static-props.md) or [`getServerSideProps`](/docs/basic-features/data-fetching/get-server-side-props.md).
+- `_error`, like `_app`, is a reserved pathname. `_error` is used to define the customized layouts and behaviors of the error pages. `/_error` will render 404 when accessed directly via [routing](/docs/routing/introduction) or rendering in a [custom server](/docs/advanced-features/custom-server).