diff --git a/test/merge_debian_isos b/test/merge_debian_isos
index 7d942179..af940d80 100755
--- a/test/merge_debian_isos
+++ b/test/merge_debian_isos
@@ -2,6 +2,10 @@
 # Copyright 2022 Thomas Schmitt <scdbackup@gmx.net> , libburnia project.
 # Provided under BSD license: Use, modify, and distribute as you like.
 
+# This obtrusive setting shall make the script safe against exotic locales.
+export LANG=C
+export LC_ALL=C
+
 usage() {
   echo "usage: $(basename "$0") result_iso mount_template iso1 iso2 [... isoN]" >&2
   echo >&2
@@ -619,7 +623,7 @@ echo "Merging package description files ..." >&2
 for i in $MOUNT_LIST
 do
   cat "$i"/md5sum.txt
-done | sort >merged_md5sum.txt
+done | sort -k 2 >merged_md5sum.txt
 
 # Determine the files which are mentioned with checksum in main Release files
 path_list=$(for i in $MOUNT_LIST
@@ -720,7 +724,8 @@ echo "Done." >&2
 echo >&2
 echo "Producing result ISO image ..." >&2
 
-# Create file with list of pool -map commands for all but the first ISO
+# Create file with list of /pool and /firmware -map commands for all but the
+# first ISO
 for mount_point in $MOUNT_LIST
 do
   if test "$mount_point" = "$mount_point_1"
@@ -731,7 +736,6 @@ do
     echo " -map ${mount_point}/pool /pool" >>temp_file
   fi
 done
-
 for mount_point in $MOUNT_LIST
 do
   if test "$mount_point" = "$mount_point_1"
diff --git a/test/merge_debian_isos.sig b/test/merge_debian_isos.sig
index 219de15f..32148eed 100644
Binary files a/test/merge_debian_isos.sig and b/test/merge_debian_isos.sig differ