diff --git a/modules/persist/default.nix b/modules/persist/default.nix
index 0baf6e63..2cfd4ba7 100644
--- a/modules/persist/default.nix
+++ b/modules/persist/default.nix
@@ -23,6 +23,11 @@ let
       };
       origin = mkOption {
         type = types.str;
+        description = ''
+          where this store is rooted within the outer filesystem.
+          conceptually, this is the store's "mount point",
+          though technically this could be a path within any larger mount.
+        '';
       };
       prefix = mkOption {
         type = types.str;