diff --git a/nix/modules/hive-c0re.nix b/nix/modules/hive-c0re.nix
index 11a51173..276f7983 100644
--- a/nix/modules/hive-c0re.nix
+++ b/nix/modules/hive-c0re.nix
@@ -38,9 +38,10 @@ in
     description = ''
       Canonical host domain for hyperhive subsystems that need a
       stable name (currently: `hyperhive.matrix.serverName` derives
-      from this when `useSubdomain = true`). No default — subsystems
-      that opt to require it assert non-null in their own config and
-      fail eval with a helpful message if it's missing.
+      from this, defaulting to `matrix.''${hyperhive.domain}` when
+      `serverName` is null). No default — subsystems that opt to
+      require it assert non-null in their own config and fail eval
+      with a helpful message if it's missing.
     '';
   };