diff --git a/writeimage.sh b/writeimage.sh
index 940af69325..8b81670e33 100755
--- a/writeimage.sh
+++ b/writeimage.sh
@@ -99,8 +99,8 @@ mkdir -p $BOOT
 
 if [ `uname` == "Darwin" ]; then
     BOOT_DEV=${SDCARD_DEV}s1 # e.g. /dev/disk4s1
-    umount ${SDCARD_DEV}* 2>/dev/null || true
-    mount_msdos $BOOT_DEV $BOOT
+    diskutil unmountDisk ${SDCARD_DEV}
+    mount -ft msdos $BOOT_DEV $BOOT
 else # assuming Linux
     BOOT_DEV=${SDCARD_DEV}p1 # e.g. /dev/mmcblk0p1
     if ! [ -e ${SDCARD_DEV}p1 ]; then
@@ -158,4 +158,3 @@ umount $BOOT
 rmdir $BOOT
 
 msg "you can now remove the sdcard"
-