diff --git a/sys/tools/embed_mfs.sh b/sys/tools/embed_mfs.sh
index a7ac80c8f8d..780ad891ae0 100644
--- a/sys/tools/embed_mfs.sh
+++ b/sys/tools/embed_mfs.sh
@@ -32,13 +32,22 @@
 # $2: MFS image filename
 #
 
+if [ $# -ne 2 ]; then
+	echo "usage: $(basename $0) target mfs_image"
+	exit 0
+fi
+if [ ! -w "$1" ]; then
+	echo $1 not writable
+	exit 1
+fi
+
 mfs_size=`stat -f '%z' $2 2> /dev/null`
 # If we can't determine MFS image size - bail.
 [ -z ${mfs_size} ] && echo "Can't determine MFS image size" && exit 1
 
 sec_info=`elfdump -c $1 2> /dev/null | grep -A 5 -E "sh_name: oldmfs$"`
 # If we can't find the mfs section within the given kernel - bail.
-[ -z "${sec_info}" ] && echo "Can't locate mfs section within kernel" && exit 1
+[ -z "${sec_info}" ] && echo "Can't locate mfs section within $1" && exit 1
 
 sec_size=`echo "${sec_info}" | awk '/sh_size/ {print $2}' 2> /dev/null`
 sec_start=`echo "${sec_info}" | awk '/sh_offset/ {print $2}' 2> /dev/null`