Can i use Modularity over a Directed graph??

Hello,
I try to find communities over a directed graph. I try using Modularity and it works, but i read that the algoritm only works over Undirected Graph, because the modularity it's calculated like if were a Undirected Graph.
Gephi makes some change to the directed Graph in order it work fine?
Maybe gephi uses a Modularity that fixes this, but i don't know how it works. I need some help.

Thanks!