diff --git a/modules/veracrypt.nix b/modules/veracrypt.nix
index 9e7607b..4dc23d7 100644
--- a/modules/veracrypt.nix
+++ b/modules/veracrypt.nix
@@ -1,7 +1,12 @@
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }:
 {
   # Looks as if TrueCrypt is unfree software
   #   https://github.com/NixOS/nixpkgs/blob/5d017a8822e0907fb96f7700a319f9fe2434de02/pkgs/applications/misc/veracrypt/default.nix#L59
+
+  # Allow installation of unfree software Veracrypt.
+  # Alternatively, run Veracrypt with
+  #   NIXPKGS_ALLOW_UNFREE=1 nix-shell -p veracrypt
+  # https://nixos.wiki/wiki/Unfree_Software
   nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
     "veracrypt"
   ];