# Font issue on using lualatex with beamer

I am trying to use beamer with lualatex to produce a presentation (MacTex 2011). Somehow, it doesn't seem to honor the font settings. See the sample below, is there anything I am missing here?

\documentclass[lualatex]{beamer}

\usepackage{fontspec}
\setmainfont{Helvetica}

\title{Something to do}

\begin{document}

\maketitle

\begin{frame}
\frametitle{I am impressed}
Text
\end{frame}
\end{document}


beamer switches by default to the sans serif font, the reason why you have to use also
\setsansfont{Helvetica}