Bug in gnop utility?

[fluffles.net]

Hello list,

I'm building offline capacity expansion support for geom_raid5, allowing 
people to add disks to an existing array, preserving all data on it. 
Currently i'm having a strange problem with GNOP, as it is refusing a 
command while i think the command is correct:

# gnop create -s 320072914432 ad18a
gnop: Invalid 'size' argument

# diskinfo -v /dev/ad18a
/dev/ad18a
        512             # sectorsize
        320072914944    # mediasize in bytes (298G)
        625142412       # mediasize in sectors

The size argument is exactly 512 bytes shorter than the device (ad18a), 
just as it should be. Maybe gnop has integer range limitations which 
prevent it from accepting this large number? That would be quite a 
disappointment, though. Any way i can workaround this? I need gnop for 
expansion. I'm running 7.0-BETA2 on AMD64. Though i need expansion 
working on i386 too. Any replies or suggestions are appreciated.

Thanks!

- Veronica