diff --git a/release/scripts/make-manifest.sh b/release/scripts/make-manifest.sh
--- a/release/scripts/make-manifest.sh
+++ b/release/scripts/make-manifest.sh
@@ -36,13 +36,25 @@
 default_kernel_dbg=on
 default_kernel_alt_dbg=off
 
+# portable sha256 command
+sha256_cmd="sha256sum"
+
+trap 'rm -rf $tmpdir' EXIT INT QUIT ABRT TERM
+tmpdir=$(mktemp -d)
+
 for i in ${*}; do
+(
 	dist="${i}"
 	distname="${i%%.txz}"
 	distname="$(echo ${distname} | tr '-' '_')"
 	distname="$(echo ${distname} | tr 'kernel.' 'kernel_')"
-	hash="$(sha256 -q ${i})"
-	nfiles="$(tar tvf ${i} | wc -l | tr -d ' ')"
+	hash="$($sha256_cmd ${i} | cut -d' ' -f1)"
+	# run with parallel xz if possible
+	if [ "$(head -c 6 ${i} | xxd -p)" = 'fd377a585a00' ]; then
+	  nfiles="$(xz -d < ${i} | tar tvf - | wc -l | tr -d ' ')"
+	else
+	  nfiles="$(tar tvf ${i} | wc -l | tr -d ' ')"
+	fi
 	default="$(eval echo \${default_${distname}:-on})"
 	desc="$(eval echo \"\${desc_${distname}}\")"
 
@@ -67,6 +79,13 @@
 			;;
 	esac
 
-	printf "${dist}\t${hash}\t${nfiles}\t${distname}\t\"${desc}\"\t${default}\n"
+	printf "${dist}\t${hash}\t${nfiles}\t${distname}\t\"${desc}\"\t${default}\n" > $tmpdir/$i
+) &
 done
 
+# run in parallel, wait for final results
+wait
+sort $tmpdir/*.txz
+
+#EOF
+