According to the manual: |--load-path=directory| Add directory *to the front* of the package module search path. This does not work for guix environment (guix 0.16.0-3.6ddc63e): Prepare to reproduce $ git clone https://gnunet.org/git/gnunet.git $ cd gnunet guix package honors --load-path: $ guix package --load-path=$PWD/contrib/guix -A gnunet [...] gnunet  v0.11.0pre66-1108-g8bb29d2fb    out     .../contrib/guix/gnu/packages/gnunet.scm:274:2 [...] guix environment still installs gnunet 0.10.1 (which is defined in guix 0.16): $ guix environment --load-path=$PWD/contrib/guix --ad-hoc gnunet [guix]$ realpath $(which gnunet-arm) /gnu/store/...-gnunet-0.10.1/bin/gnunet-arm Using GUIX_PACKAGE_PATH the correct version of gnunet is installed into the environment: $ export GUIX_PACKAGE_PATH=$PWD/contrib/guix $ guix environment --ad-hoc gnunet [guix]$ realpath $(which gnunet-arm) /gnu/store/...-gnunet-v0.11.0pre66-1108-g8bb29d2fb/bin/gnunet-arm -- Regards Hartmut Goebel | Hartmut Goebel | h.goebel@crazy-compilers.com | | www.crazy-compilers.com | compilers which you thought are impossible |