Actor Peter Sarsgaard was left feeling even more awkward than usual during sex scenes for his new movie because his mother-in-law was directing the shoot.

Screenwriter Naomi Foner has made her directorial debut with Very Good Girls, and hired her daughter Maggie Gyllenhaal's partner to star in the movie, about two teens desperate to lose their virginity.

Sarsgaard's character embarks on an affair with Dakota Fanning in the film, and the actor admits playing the raunchy role was hard to do in front of his wife's mother.

He tells E! news, "(It was) Bizarre, totally bizarre. I hadn't read it that carefully, so I didn't realize I was going to be doing a sex scene. So that was the real surprise. Maggie and I kind of realised it at about the same time that I would be doing that.

"But you know, my mother-in-law's asking me to be in a movie that she's directing. I didn't have the same scrutiny about the project I would have with something else. So I missed that part, and also the fact that it was with Dakota Fanning."