Giovanni Ribisi has signed up to join Johnny Depp in The Rum Diary, the adaptation of legendary gonzo journalist Hunter S. Thompson's memoir of his time in Puerto Rico during the 1950s.

The film's been in development for years - Depp's been trying to make it since 2000 - but perhaps that's appropriate given that the book sat on Thompson's shelf for 40 years after it was written after being rejected by a raft of publishers. However, now things are under way: Bruce Robinson (Withnail & I, Happy Feet) is writing and directing, and the cast is almost set.

Depp is playing washed-up journalist Paul Kemp; Amber Heard is playing Chenault, the free-spirit who dates a colleague but becomes involved with Kemp as well; Aaron Eckhart is the wealthy Sanderson and recent Oscar nominee Richard Jenkins is paper editor Lotterman. It's not clear yet who Ribisi will play - we're guessing either Moberg or Yeamon - but we do know he's a "carousing journalist", one of what Thompson called the "ill-tempered, wandering rabble" who staffed the backwater paper.

Filming starts in Puerto Rico on Wednesday. And hey! At least now when Jack Sparrow asks "But where has rum gone?" we'll know the answer.