diff --git a/common.sh.in b/common.sh.in
index d21ed0c..db1bc5d 100644
--- a/common.sh.in
+++ b/common.sh.in
@@ -101,9 +101,9 @@ format_disk0() {
   if sfdisk --help | fgrep -q -- '--no-reread'; then
     ARGS="--no-reread $ARGS"
   fi
-
+  ARGS="--label dos $ARGS"
   sfdisk $ARGS --quiet "$1" <<EOF
-${PARTITION_ALIGNMENT},,L,*
+1M,,L,*
 EOF
 }
 
@@ -127,6 +127,18 @@ map_disk0() {
 
 unmap_disk0() {
   kpartx -d -p- $1
+
+  if sfdisk --help | fgrep -q -- '--no-reread'; then
+    ARGS="--no-reread $ARGS"
+  fi
+
+  # loopback device has correct 512b blocks
+  blockdev=$(losetup --show -f $1)
+  sfdisk $ARGS --delete "$blockdev"
+  sfdisk $ARGS --label dos --quiet $blockdev <<EOF
+2048,,L,*
+EOF
+  losetup -d $blockdev
 }
 
 cleanup() {