diff --git a/build b/build
index b38c711..c1bd05a 100755
--- a/build
+++ b/build
@@ -32,11 +32,9 @@ main()
 	version) printf "%s\nWebsite: %s\n" "$relname" "$projectsite" ;;
 	release) shift 1; mkrelease $@ ;;
 	roms)
-		if [ $# -gt 1 ] && [ "$2" = "serprog" ]; then
-			x_ ./mk -b stm32-vserprog
-			x_ ./mk -b pico-serprog; return 0
-		fi; shift 1
-		x_ ./mk -b coreboot $@ ;;
+		[ $# -gt 1 ] && [ "$2" = "serprog" ] && \
+		    mk -b stm32-vserprog pico-serprog && return 0
+		shift 1; x_ ./mk -b coreboot $@ ;;
 	*)
 		[ -f "$spath" ] || $err "bad command"
 		$shcmd; "$spath" $@ || $err "excmd: $spath $(echo "$@")" ;;
@@ -105,9 +103,7 @@ build_release()
 	touch "$srcdir/lock" || $err "can't make lock file in $srcdir/"
 	(
 	cd "$srcdir" || $err "$vdir: 2 !cd \"$srcdir\""
-	./mk -b coreboot || $err "$vdir: roms-all"
-	./mk -b pico-serprog || $err "$vdir: rp2040"
-	./mk -b stm32-vserprog || $err "$vdir: stm32"
+	mk -b coreboot pico-serprog stm32-vserprog
 	x_ mv bin ../roms
 	) || $err "can't build rom images"
 
diff --git a/include/lib.sh b/include/lib.sh
index 586ecde..2c9cd0d 100644
--- a/include/lib.sh
+++ b/include/lib.sh
@@ -212,3 +212,11 @@ cbfs()
 	lzma="-c lzma" && [ $# -gt 3 ] && lzma="-t raw"
 	x_ "$cbfstool" "$1" $ccmd -f "$2" -n "$3" $lzma
 }
+
+mk()
+{
+	mk_flag="$1" || $err "No argument given"
+	shift 1 && for mk_arg in $@; do
+		./mk $mk_flag $mk_arg || $err "./mk $mk_flag $mk_arg"; :
+	done; :
+}
diff --git a/script/trees b/script/trees
index 227b221..01df28a 100755
--- a/script/trees
+++ b/script/trees
@@ -36,9 +36,7 @@ main()
 		project="${OPTARG#src/}"; shift 2
 	done
 	[ -z "$_f" ] && $err "missing flag (-m/-u/-b/-c/-x/-f/-s/-l/-n)"
-	[ -z "$project" ] && for p in $(ls -1 config/git); do
-		./mk $_f "$p" || $err "!./mk $_f $p"; :
-	done && return 1
+	[ -z "$project" ] && mk $_f $(ls -1 config/git) && return 1
 
 	[ -f "config/git/$project/pkg.cfg" ] || $err "'$project' not defined"