Merge error?

When I write this line
<%= :round, :action, ["a", "b", "c", "d"] %>

I get this. What gives?
undefined method `merge' for ["a", "b", "c", "d"]:Array

Round is my model and action is a field in that model. I simply want
to be able to set that field to a b c or d.

I'm guessing round_form is the form builder yielded by a form_for, in
which (case at least from the name) it's already bound to round - you
can just say :action, ["a", "b", "c", "d"] Right
now rails is assuming your last argument is a hash of options