Rogue One‘s composer Michael Giacchino had a very short time to make the music for the first ever Star Wars anthology movie.

Not only is Rogue One the first Star Wars film that doesn’t feature John Williams’ iconic score, but composer Michael Giacchino wasn’t given a lot of time to build a brand new soundtrack for the universe.

Giacchino, whose work includes Star Trek, Inside Out and Lost, was brought in to replace Alexandre Desplat, who dropped out due to a scheduling conflict. Giacchino had very little time to score the film, however, having just finished Marvel’s Doctor Strange and gearing up to do Spider-Man: Homecoming.

In an interview with EW, the composer says:

I saw the film and I really, really, really enjoyed it, so there was no lack of ideas or inspiration, that’s for sure. The only worry the whole time for me was just the schedule … At the time, it left me with literally four and a half weeks to write. But I mapped it out and I thought, okay, if I do this much a day and I get this done that will leave me time to go back and improve if I need to before having to orchestrate.

At the time he began working on the score, Desplat had already composed some music, but Giacchino chose not to listen to it. “I was like, ‘No, I don’t want to. I want nothing, nothing. Let’s just do it,'” he says.

Not only will Rogue One not have the traditional title crawl, but Giacchino also confirms that there’ll be a completely different score over the opening credits. But there’ll also be nods to Williams, including a new version of the Imperial March.

A big Star Wars geek himself, Giacchino says he had a great time on the project despite the time crunch. When asked his opinion about Rogue One, here’s what he had to say:

It is a film that is in many ways a really great World War II movie, and I loved that about it. But it also has this huge, huge heart at the center of it, and that was the one thing I just didn’t want to discount. Yes, it’s an action movie, and it’s a Star Wars film, and it has all the things that you would come to expect and love about that, but I didn’t want to forget that it was also an incredibly emotional movie as well. That was what really pulled me in. I love working on projects that have an emotional center to them – and not manufactured emotion either, even though, you know, [laughs] it’s a weird thing to say because literally that’s all we’re doing, manufacturing emotion.

‘Rogue One: A Star Wars Story’ hits theaters on December 16