https://lintian.debian.org/tags/init.d-script-does-not-source-init-functions.html

Index: guix-debian/etc/init.d/guix-daemon.in
===================================================================
--- guix-debian.orig/etc/init.d/guix-daemon.in
+++ guix-debian/etc/init.d/guix-daemon.in
@@ -16,6 +16,9 @@ then
   exit 5
 fi
 
+# Source common functions used by init scripts in Debian
+. /lib/lsb/init-functions
+
 case "$1" in
 start)
   if [ -f "/var/run/guix-daemon.pid" ]
