Compatibility between sansmath and fontaxes

See the following MWE:

documentclass{article}
usepackage{sansmath}
usepackage{fontaxes}
begin{document}
$123$
sansmath
$123$
mathweight{normal}
$123$
end{document}

The mathweight{normal} command somehow seems to unset the sans font. I get the following output:

Additionally the following warning is printed:

Package fontaxes Warning: I don't know how to decode
(fontaxes)                math `sans' on input line 8.

I guess I somehow have to tell fontaxes about the sans font, but I don’t know how to do that.