Farrell turned to pals in the New York Police Department for help when he was cast as bad cop Jimmy Egan in Gavin O'Connor's new movie.
But the Irish star - who has a home in Manhattan's East Village - is nervous about their reaction when they discover how corrupt Egan really is.
Farrell tells the New York Daily News, "I'll keep the engine running tonight, that's for sure. 'Cause I told them I was a dirty cop, but I didn't tell them how rank (bad) I was."
Source: WENN