Need help: using alt_inbuf with StratixII GX lvds inputs and Quartus II

When I try to use the following:

hsm2: alt_inbuf

port map(

i => hsm_rx_d_p(2),

o => my_output);

I get an error message about O not being connected, even though

"my_output" is declared as being a signal. What is the correct way to

get LVDS inputs into a design? I cannot use alt_inbuf_diff, since it is

not compatible with Stratix II GX.

Thanks