sfrb usage in structures

I'm using Crossworks v2.21 for MSP430. I have a common uart driver which gets passed a control & I wish to add some sfrb's to it. When I do this:

sfrb my_sfr = UCA0TXBUF_;

this is OK and usable. However, as I need this in a structure, I tried:

typedef struct
{
sfrb TX_BUFF;

} Reg_t;

but this will not compile, giving:

error E2088: invalid struct field declaration
error E2000: found 'sfrb', expecting '}'

Is there a way to use sfrb's in structures or a workaround to this?

Paul