How to make sphinx look for modules in virtualenv while building html?

The problem is correctly spotted by Mathijs.

$ which sphinx-build
/usr/local/bin/sphinx-build

I solved this issue installing sphinx itself in the virtual environment.

With the environment activated:

$ source /home/migonzalvar/envs/myenvironment/bin/activate
$ pip install sphinx
$ which sphinx-build
/home/migonzalvar/envs/myenvironment/bin/sphinx-build

It seems neat enough.