HP 1800-8G- It says I need to assign at least two ports to create a Trunk...Is this right?

I'm chugging along creating my VLANS, assigning ports, then I get to Trunk Membership...All I want/need is one Trunk port (which will go to my PfSense). When I choose port eight and I apply, I get an error stating that "T1 contains only one port. Please ensure that each trunk contains at least two ports AND no more than eight ports". Any idea why?