Brad Pitt's World War Z is set to undergo a script rewrite and extensive reshoots even though filming has ended.

The actor - who is also one of the producers - shot the post-apocalyptic horror film in various locations around Europe last year but Prometheus screenwriter Damon Lindelof has been brought on board to fix some problems with the first cut. Lindelof is thought to be concentrating on the film's third act which reportedly needs serious restructuring.

The December 2012 release date has been pushed back to summer 2013 to allow for six to seven weeks of reshoots in September and October.

The movie is based on the 2006 novel by Max Brooks and also stars Mireille Enos, James Badge Dale, and Anthony Mackie. Marc Forster has directed the film.

The reshoots will be a blow to the studio Paramount, who had hoped to turn it into a trilogy.