diff --git a/archivers/xzize.sh b/archivers/xzize.sh
index 09d9ea9..b3b82fc 100755
--- a/archivers/xzize.sh
+++ b/archivers/xzize.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# xzize.sh, Copyright © 2010 Matteo Cypriani
+# xzize.sh, Copyright © 2010, 2019 Matteo Cypriani
 #
 # This program is free software. It comes without any warranty, to
 # the extent permitted by applicable law. You can redistribute it
@@ -16,12 +16,12 @@
 # file is removed.
 # If the file is already XZ compressed (.xz, .txz), nothing is done.
 
-
+#set -x
 set -u
 
 # Destination file suffix when source file name suffix is a
 # 3-letter compressed tar suffix:
-TAR_XZ_EXT=txz
+readonly TAR_XZ_EXT=txz
 
 # Default compression level:
 COMPRESSION_LEVEL=
@@ -83,63 +83,63 @@ for SOURCE in "$@" ; do
 
 	# GZip
 	if test_extension "$SOURCE" gz ; then
-		ACTION=gunzip
+		ACTION="gunzip"
 		do_recompress
 		continue
 	fi
 
 	# GZipped Tar (.tgz)
 	if test_extension "$SOURCE" tgz $TAR_XZ_EXT ; then
-		ACTION=gunzip
+		ACTION="gunzip"
 		do_recompress
 		continue
 	fi
 
 	# BZip2
 	if test_extension "$SOURCE" bz2 ; then
-		ACTION=bunzip2
+		ACTION="bunzip2"
 		do_recompress
 		continue
 	fi
 
 	# BZipped Tar (.tbz)
 	if test_extension "$SOURCE" tbz $TAR_XZ_EXT ; then
-		ACTION=bunzip2
+		ACTION="bunzip2"
 		do_recompress
 		continue
 	fi
 
 	# BZipped Tar (.tb2)
 	if test_extension "$SOURCE" tb2 $TAR_XZ_EXT ; then
-		ACTION=bunzip2
+		ACTION="bunzip2"
 		do_recompress
 		continue
 	fi
 
 	# LZMA
 	if test_extension "$SOURCE" lzma ; then
-		ACTION=unlzma
+		ACTION="unlzma"
 		do_recompress
 		continue
 	fi
 
 	# LZMA compressed Tar (.tlz)
 	if test_extension "$SOURCE" tlz $TAR_XZ_EXT ; then
-		ACTION=unlzma
+		ACTION="unlzma"
 		do_recompress
 		continue
 	fi
 
 	# Compress
 	if test_extension "$SOURCE" Z ; then
-		ACTION=uncompress
+		ACTION="uncompress"
 		do_recompress
 		continue
 	fi
 
 	# Compressed Tar (.taz)
 	if test_extension "$SOURCE" taz $TAR_XZ_EXT ; then
-		ACTION=uncompress
+		ACTION="uncompress"
 		do_recompress
 		continue
 	fi