expl3 with check-declarations turned on fails to compile if siunitx is loaded

It's “Hi, Joseph!”

The first error is due a typo in siunitx.sty. At line 4584 (release 2.6q dated 2016/03/01) the package has

\bool_new:N \l__siunitx_two_parts_bool

instead of

\bool_new:N \l__siunitx_per_two_parts_bool

The variable \l__siunitx_product_repeat_bool is indeed undeclared.

Well, either disable the check again or add the two missing variables manually:

\documentclass{article}
\usepackage[check-declarations]{expl3}
\ExplSyntaxOn
\bool_new:N \l__siunitx_per_two_parts_bool
\bool_new:N \l__siunitx_product_repeat_bool
\ExplSyntaxOff
\usepackage{siunitx}
\begin{document}
Either I am using package expl3 inappropriately, or it's Hi Joseph!
\end{document}

The check is meant really for testing purposes only.