The actor plays a country music performer alongside Gwyneth Paltrow in the film, and writer/director Shana Feste decided on an unusual method of testing out her leading man's vocal abilities.
Feste took Hedlund to the Brass Monkey bar in Los Angeles, where they had a few drinks before she encouraged him to take the stage.
She tells the Hollywood Reporter, "Garrett auditioned in a karaoke bar. It was not very conventional. But I had never heard him sing and he was really nervous and singing for the first time.
"We wanted to make it really fun... We had a few drinks and he got up there and started singing and was definitely not the sound that he is at now, which is amazing, because he literally went from singing a Pearl Jam song to singing country like the best of them."