diff --git a/doc/notfound.md b/doc/notfound.md
index f5447a6..1125404 100644
--- a/doc/notfound.md
+++ b/doc/notfound.md
@@ -2,7 +2,7 @@
 
 # Unknown command
 
-The Unknown Command reply (421, ERR_UNKNOWNCOMMAND in RFC 1459) is when the server doesn't recognise a command a client sends.
+The Unknown Command error (421, ERR_UNKNOWNCOMMAND in [RFC 1459](https://datatracker.ietf.org/doc/html/rfc1459#section-6.1)) is when the server doesn't recognise a command a client sends.
 
 ```
 ↗️ UNKNOWNCMD :something