strange warning when using newtxmath and siunitx packages together

I've just noticed that I'm compiling my documents I get something similar to the following warning:

LaTeX Font Warning: Font shape OT1/cmr/m/n' in size <5.5> not available
(Font)              size <5> substituted on input line 6.


I'm not worrying too much as it's "just" a warning. My MWE is as follows:

\documentclass{article}

\usepackage{siunitx}
\usepackage{newtxmath}

\begin{document}
hello world
\end{document}


I was originally using the memoir package and not the Computer Modern fonts and still getting a similar error message about CM fonts. Which is why I originally noticed it. Hacked down my list of packages a lot and this is all that seem to be needed to show the behaviour. The order doesn't seem to matter, and the warning always points to the \begin{document}—I presume some code from one of the packages is running there?

Just had more of a read through the scroll back, and see a number of similar warnings for different fonts.

• If you use fix-cm (or the older type1cm) package latex will know that cm fonts are scalable these days and scale to the requested size – David Carlisle Nov 15 '13 at 19:51
• Great, works well in my example and real code. Thanks! Do you want to post this as an answer so it can be closed? – Sam Mason Nov 15 '13 at 20:21

If you use fix-cm (or the older type1cm`) package latex will know that cm fonts are scalable these days and scale to the requested size.