Problems with alias commands for \tabularnewline

I'm not sure if siunitx can do something about it, but I just came across this problem in a document which uses the ctable package:

\documentclass{book}
\usepackage{siunitx}


\begin{document}
%works:
\begin{tabular}{lS}
abc & 1.230\textsuperscript{*} \tabularnewline
\end{tabular}

\begin{tabular}{lS}
abc & 1.230\textsuperscript{*} \\
\end{tabular}

%fails
\def\NN{\tabularnewline}

\begin{tabular}{lS}
abc & 1.230\textsuperscript{*}\NN
\end{tabular}

\end{document}