Encrypted swap not mount on boot

swapon: /dev/mapper/cryptswap1: stat failed: No such file or directory

I use option offset=4096 in file /etc/crypttab.

# cat /etc/crypttab
cryptswap1 UUID=73bdb3b5-7c82-4a86-a6fd-7219f42c87b3 /dev/urandom swap,cipher=aes-cbc-essiv:sha256,offset=4096

Don't forget:
# update-initramfs -u