In the four decades that Star Wars has dominated pop culture, we’ve never had to hear a soundtrack for a live-action movie that wasn’t written by John Williams. Williams wrote the original trilogy, and then the follow-up prequels, and even dove back in for the soundtrack for Star Wars: The Force Awakens. So the fact that Williams did not write the music for Rogue One: A Star Wars Story is just one of many ways in which Rogue One represents a departure from the main story. No Star Wars crawl, no John Williams, no problem? I guess we’ll see.

Somehow, though, Rogue One composer Michael Giacchino has found replacing John Williams to be the second hardest thing about the project. In a recent interview with Entertainment Weekly (via the A.V Club.), Giacchino admitted that he had only four weeks to write the full Rogue One score after Alexandre Desplat was forced to leave during reshoots. In the wide-ranging interview, Giacchino talks freely about agreeing to join Rogue One at the last minute and mountain of pressure this put him under.

Yes, literally the last thing I expected I’d be doing this month would be this. I mean we were literally planning a vacation when I got the call asking if I could come and talk to them about it. At the time, it left me with literally four and a half weeks to write. … I spent the weekend with my kids and said, “You know what? The next four and a half weeks are going to be brutal. But Monday I’m going to start it,” and Monday I sat down and started it. And there it was: four and a half weeks later, we were scoring.

While this all might seem like a reason for Star Wars fans to panic, writing music can often be more of a mathematical process than an artistic one. Every composer worth their salt has musical ideas written down in various places  —  chord progressions and melodies they hope to work into future projects  —  making even a major project like Rogue One a practical combination of pulling old ideas, combining them with preexisting music, and introducing a few new concepts along the way. As long as Giacchino’s Rogue One score isn’t just the audio of Bill Murray singing the Star Wars theme song on Saturday Night Live, we should be pretty happy with the results.

Rogue One: A Star Wars Story hits theaters on December 16, 2016.

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