Sphinx documentation: how to disable default argument extension?

Question

I have some features like

f(x, propagation_speed=scipy.constants.c)

I run sphinx-apidocto create documentation on them and make htmlget them to get the final HTML data.

Alas, the Sphinx extends constants and gives me something like

f(x, propagation_speed=299792458.0)

Can't I somehow disable the default extension in docstrings? Can I add something to conf.py?