diff -ur grub-2.04.orig/util/grub-mkconfig.in grub-2.04/util/grub-mkconfig.in
--- grub-2.04.orig/util/grub-mkconfig.in	2019-08-18 15:49:45.245000000 +0200
+++ grub-2.04/util/grub-mkconfig.in	2019-08-18 15:49:57.907000000 +0200
@@ -1,5 +1,6 @@
 #! /bin/sh
 set -e
+set -o posix
 
 # Generate grub.cfg by inspecting /boot contents.
 # Copyright (C) 2006,2007,2008,2009,2010 Free Software Foundation, Inc.