Units in matplotlib

When printing in matplotlib a pint quantity wich has units, e.g.

title=(f'Effect of $d_M$ (Radius = {radius:.0f~L})')
fig.suptitle(title)

the ascii character µ is not recognized because it is defined as:

micron = micrometer = µ

in ~/.local/lib/python3.6/site-packages/pint/default_en.txt

However it is rendered correctly if it is defined as:

micron = micrometer = \mu m = µm