diff --git a/docs/third_party/mailman3/third_party-mailman3.en.md b/docs/third_party/mailman3/third_party-mailman3.en.md
index 5bb8b8c59..69f4d3ebc 100644
--- a/docs/third_party/mailman3/third_party-mailman3.en.md
+++ b/docs/third_party/mailman3/third_party-mailman3.en.md
@@ -83,7 +83,7 @@ apt install certbot
 Get the desired certificates (as *root* or *sudo*):
 
 ```
-certbot certonly -d mailcow_HOSTNAME
+certbot certonly -d MAILCOW_HOSTNAME
 certbot certonly -d MAILMAN_DOMAIN
 ```