diff --git a/howto/gitlab.md b/howto/gitlab.md
index 0f01683c33bbf0f7d958a9b8c55d85f01ec1f67d..ca87d6b7c8e953ec7b50a25da3b7da68043e7b16 100644
--- a/howto/gitlab.md
+++ b/howto/gitlab.md
@@ -269,8 +269,10 @@ URL should be:
 ... and you should select the notifications you wish to see in
 `#tor-bots`. You can also enable notifications to other channels by
 adding more parameters to the URL, like (say)
-`?channel=%23tor-foo`. The parameters are documented the [KGB
-documentation](https://salsa.debian.org/kgb-team/kgb/-/wikis/usage).
+`?channel=tor-foo`. Important note: do not try to put the `#` in
+the channel name, or if you do, URL-encode it (e.g. like `%23tor-foo`),
+otherwise this will silently fail to change the target channel. Other
+parameters are documented the [KGB documentation](https://salsa.debian.org/kgb-team/kgb/-/wikis/usage).
 
 Note that GitLab admins might be able to configure [system-wide
 hooks](https://gitlab.torproject.org/help/system_hooks/system_hooks) in [the admin section](https://gitlab.torproject.org/admin/hooks), although it's not entirely clear