JFFS2: "Magic bitmask 0x1985 not found"

mkfs.jffs2  -s 0x20000 -e 0x20000 -p 0x400000 -d  ./rootfs -o rootfs.jffs2

flash_eraseall -j /dev/mtd2
dd if=rootfs.jffs2 of=/dev/mtdblock2

mount -t jffs2 /dev/mtdblock2 /mnt


I cannot mount JFFS2 and see "Magic bitmask 0x1985 not found" messages

http://www.linux-mtd.infradead.org/faq/jffs2.html
http://www.linux-mtd.infradead.org/faq/jffs2.html#L_magicnfound