diff --git a/docs/Reference/Server.md b/docs/Reference/Server.md
index 77e7805b41..1af2057c8e 100644
--- a/docs/Reference/Server.md
+++ b/docs/Reference/Server.md
@@ -1426,6 +1426,13 @@ plugins are registered. If you would like to augment the behavior of the default
 arguments `fastify.setNotFoundHandler()` within the context of these registered
 plugins.
 
+> Note: Some config properties from the request object will be 
+> undefined inside the custom not found handler. E.g:
+> `request.routerPath`, `routerMethod` and `context.config`. 
+> This method design goal is to allow calling the common not found route.
+> To return a per-route customized 404 response, you can do it in
+> the response itself.
+
 #### setErrorHandler
 <a id="set-error-handler"></a>