diff --git a/nixos/modules/services/torrent/transmission.nix b/nixos/modules/services/torrent/transmission.nix
index b16f5c97fe4bb..5c87da3af93e0 100644
--- a/nixos/modules/services/torrent/transmission.nix
+++ b/nixos/modules/services/torrent/transmission.nix
@@ -189,6 +189,10 @@ in
           and [](#opt-services.transmission.settings.watch-dir).
           Note that you may also want to change
           [](#opt-services.transmission.settings.umask).
+
+          If `null`, the home and the download directories become
+          world-readable. This isn't recommended, and instead relevant users
+          should be added to the `transmission` group.
         '';
       };