Can't define fixed-width font with TexShop, fontspec

Question

I've used Alex Hirzel's code to enable code snippets in LaTex articles:

The problem is that I can't set the font to a fixed-width one. Whenever this line is commented out:

%\fontspec{Courier New}

I get the following error:

./code3.tex:33: Undefined control sequence.
\codefont -> \fontspec 
                       {Courier New} \fontsize {9pt}{11pt}\selectfont 
l.33 \begin{code}

Any idea how can I set the font type? I'm using TexShop on Mac, if it matters.

Answer 1

Load the fontspec package (and naturally compile then with xelatex or lualatex).