gpart trouble

[bob prohaska]

I want to add some swap partitions to the June 28th RPI3 snapshot image on microSD. 
Growfs was suppressed, so the card has 12 GB of free space:

Enter full pathname of shell or RETURN for /bin/sh: 
Cannot read termcap database;
using dumb terminal settings.
# mount -o rw /
# gpart show mmcsd0
=>      63  31116225  mmcsd0  MBR  (15G)
        63      2016          - free -  (1.0M)
      2079    102312       1  fat32lba  [active]  (50M)
    104391   5138469       2  freebsd  (2.5G)
   5242860  25873428          - free -  (12G)

# gpart add -t freebsd-swap -s 1G mmcsd0
gpart: Invalid argument
# gpart add -t freebsd-swap -s 1G /dev/mmcsd0
gpart: Invalid argument
# gpart add -t freebsd-swap -s 1GB -l swap mmcsd0
gpart: Invalid argument
# 

It seems to me this worked with an earlier snapshot, has something changed?

Thanks for reading!

bob prohaska