When Will Gluck signed on to direct Annie, he knew he wanted to update the music.
So he recruited songwriters Sia and Greg Kurstin to give the classic musical a modern-day feel.
“Sia is awesome,” Gluck tells PEOPLE. “I was super lucky that she was interested and she loved Annie as a kid.”
While the “Chandelier” singer was initially only supposed to write a song or two for the film, Gluck eventually convinced her to come onboard for the whole thing.
“She’s so fun to work with,” he adds.
Sia and Kurstin wrote three entirely new songs for the movie, which stars Beasts of the Southern Wild actress Quvenzhané Wallis as the orphan girl with a heart of gold.
Gluck’s favorite song by far, however, is “Opportunity.”
“Annie sings this song after she realizes that she’s got a good thing going with Jamie Foxx‘s character,” he says. “She goes to the Guggenheim Museum and they ask her to give a speech, but instead she just sings a song about what a great opportunity she’s been given.”
The scene’s a real tearjerker in a movie that’s full of them, says Gluck. “The crew couldn’t stop crying! It’s the song that all the guys start weeping to.”
Annie is out Dec. 19. Check out the exclusive video below: