Filter design, complex specification

Hi,

I am trying to design a filter using firls (b = firls(n,f,a)), but in my case the 'a' vector is complex. In other words I am specifying both the amplitude and phase of the ideal filter. I am getting a complex filter. However, if I use fir2 instead, I get a real filter.

Is is 'legitimate' to use complex input for firls?

Thanks, Silviu.