Character mistake: When Lucian tells Vlad that the creature he encountered is a vampire, Lucian says that "Pi" is Greek for "to drink". "Pi" is actually the Albanian word for drink, not Greek.
Character mistake: At the end of the movie, when Jaggu is listening to the sounds recorded by PK, the audio contains the question which she asked, "Tumhare planet pe sab aise hi hote, bade kan wale?" but does not contain the answer which PK gave, even though he was sitting right there. This seems to suggest that PK did not exist in the real world.
Character mistake: During the scene at the office of the University of Oxford, the Union Jack is hanged the opposite way from the proper position. (01:23:10)