diff --git a/guix.scm b/guix.scm
index e21f36f..55879c5 100644
--- a/guix.scm
+++ b/guix.scm
@@ -1,13 +1,15 @@
 (use-modules (guix packages)
              ((guix licenses) #:prefix license:)
              (guix build-system python)
+             (guix download)
              (gnu packages)
              (gnu packages pkg-config)
              (gnu packages python-xyz)
              (gnu packages python))
 
 ;; this file allows reproducible builds
-;; execute `guix environment -l guix.scm' to get an working environment
+;; execute `guix time-machine --commit=e534919c1e6c15bf38475060a59e1c1b7b68fdf3 -- environment -l guix.scm'
+;; to get an working environment
 
 
 (define-public python-mkdocs-material-6