diff --git a/Makefile b/Makefile
index e1b64d949..9d3e59cc7 100644
--- a/Makefile
+++ b/Makefile
@@ -32,7 +32,7 @@ dsk: asm index
 	cp res/_FileInformation.txt build/
 	$(CADIUS) ADDFILE build/"$(DISK)" "/$(VOLUME)/" build/LAUNCHER.SYSTEM >>build/log
 	cp res/PREFS.CONF build/PREFS.CONF
-	bin/padto.sh 512 build/PREFS.CONF >>build/log
+	bin/padto.sh build/PREFS.CONF
 #
 # create _FileInformation.txt files for subdirectories
 #
@@ -105,7 +105,7 @@ dsk: asm index
 	done
 	bin/changebootloader.sh build/"$(DISK)" build/proboothd
 
-index: md
+index: md asmfx asmprelaunch
 # note: even though individual lines check individual files, you really want
 # to re-run this with a clean build/ directory if anything changes, because
 # everything is interconnected within TOTAL.DATA
diff --git a/bin/padto.sh b/bin/padto.sh
index 1721ab3d3..273ec6d55 100755
--- a/bin/padto.sh
+++ b/bin/padto.sh
@@ -1,11 +1,5 @@
 #!/bin/bash
 
-totalsize=$1
-outfile=$2
+# zero-pads $1 to a multiple of 512 bytes, in place
 
-[[ "$OSTYPE" == "linux-gnu" ]] \
-    && filesize=$(stat -c "%s" "$outfile") \
-    || filesize=$(stat -f "%z" "$outfile")
-
-padsize=$((512-$filesize))
-dd if=/dev/zero bs=1 count=$padsize 2>/dev/null >> "$outfile"
+dd if=/dev/null of="$1" bs=1 count=1 seek="$((($(wc -c < "$1") + 511) & -512))" 2>/dev/null