Dear, Just a heads-up to say that this still applies to 27.1.
--8<---------------cut here---------------start------------->8--- guix describe Generation 86 Sep 09 2020 12:21:38 (current) guix ce022b2 repository URL: https://git.savannah.gnu.org/git/guix.git commit: ce022b2e142c75b9e4d05fc1aec91e345dc374a7 guix time-machine --commit=057d584b98 -- build emacs --no-grafts [...] /gnu/store/wn1m7lwnasvwygbaf8ky413qzbm96mys-emacs-27.1 guix time-machine --commit=057d584b98 \ -- build emacs --check --no-grafts [...] guix build: error: derivation `/gnu/store/s9avsbm004zjrkba9v58ricy2vk56gzz-emacs-27.1.drv' may not be deterministic: output `/gnu/store/wn1m7lwnasvwygbaf8ky413qzbm96mys-emacs-27.1' differs --8<---------------cut here---------------end--------------->8--- Then the files that differ are: --8<---------------cut here---------------start------------->8--- diff -r --no-dereference /gnu/store/wn1m7lwnasvwygbaf8ky413qzbm96mys-emacs-27.1{,-check} Binary files /gnu/store/…-emacs-27.1/libexec/emacs/27.1/x86_64-pc-linux-gnu/emacs.pdmp and /gnu/store/…-emacs-27.1-check/libexec/emacs/27.1/x86_64-pc-linux-gnu/emacs.pdmp differ Binary files /gnu/store/…-emacs-27.1/share/emacs/27.1/lisp/cedet/semantic/lex-spp.elc and /gnu/store/…-emacs-27.1-check/share/emacs/27.1/lisp/cedet/semantic/lex-spp.elc differ Binary files /gnu/store/…-emacs-27.1/share/emacs/27.1/lisp/cedet/semantic/tag-file.elc and /gnu/store/…-emacs-27.1-check/share/emacs/27.1/lisp/cedet/semantic/tag-file.elc differ Binary files /gnu/store/…-emacs-27.1/share/emacs/27.1/lisp/cedet/semantic/tag-ls.elc and /gnu/store/…-emacs-27.1-check/share/emacs/27.1/lisp/cedet/semantic/tag-ls.elc differ Binary files /gnu/store/…-emacs-27.1/share/emacs/27.1/lisp/cedet/semantic.elc and /gnu/store/…-emacs-27.1-check/share/emacs/27.1/lisp/cedet/semantic.elc differ Binary files /gnu/store/…-emacs-27.1/share/emacs/27.1/lisp/gnus/mm-extern.elc and /gnu/store/…-emacs-27.1-check/share/emacs/27.1/lisp/gnus/mm-extern.elc differ --8<---------------cut here---------------end--------------->8--- All the best, simon