The trailer for the upcoming Harry Potter and the Sorcerer's Stone shows apprentice wizard Harry riding a broom with the brush part behind him.
"Warner Bros. claims the film is an accurate portrayal of things that happen in witchcraft, yet woodcuts from the 16th and 17th centuries show broomsticks being ridden with the brush part in the front,'' Kevin Carlyon told Reuters.
"It's a common mistake--even the '60s TV series 'Bewitched' showed broomsticks being ridden backwards--but this is not correct."
Carlyon, who claims he owns three riding brooms, runs his own coven in Sussex, in the south of England.
Expected to be released in November, Harry Potter and the Sorcerer's Stone is based on the best-selling novel by JK Rowling.