lua-unicode-math cannot find \ohm

[teepeemm]

\documentclass{article}
\usepackage{lua-unicode-math}
\usepackage{siunitx}
\begin{document}
Ohm: \unit{\ohm}, $\unit{\ohm}$
\end{document}

Causes "Missing character: There is no Ω (U+03A9) in font cmr10!", and neither appears in the output.

It's ok with just unicode-math.

[josephwright]

OK, I see why this is happening: I'm thinking about the best solution.