changing serial port speed

[Unprivileged user <nobody_(_at_)_foghorn_(_dot_)_aseq_(_dot_)_com>]

I'm trying to change the serial port speed from the default of 9600 to 2400.

Celeron 600 MHz, Openbsd 3.2, dmesg reports
pccom0 at isa0 port 0x3f8/8 irq 4: ns16550a, 16 byte fifo
pccom1 at isa0 port 0x2f8/8 irq 3: ns16550a, 16 byte fifo

Serial ports are not currently used for anything, and /etc/ttys lists them as:
tty00   "/usr/libexec/getty std.9600"   unknown off
tty01   "/usr/libexec/getty std.9600"   unknown off

# stty -f /dev/cua00
speed 9600 baud;
lflags: echoe echoke echoctl
cflags: cs8 -parenb
# stty -f /dev/cua00 speed 2400
9600
# stty -f /dev/cua00
speed 9600 baud;
lflags: echoe echoke echoctl
cflags: cs8 -parenb

I've tried this with cua01, tty00 and tty01, but no success. Shouldn't stty change 
the serial port speed?