diff --git a/types.nix b/types.nix
index b214450..bf3461b 100644
--- a/types.nix
+++ b/types.nix
@@ -208,6 +208,7 @@ rec {
         in
           isString x && (x == "/" || (length xs > 0 && all filename.check xs));
       merge = mergeOneOption;
+      description = "A path name";
     };
   };