Hopefully some technical wizardry will mean Harry Potter fans don't notice the difference in the film.
But as these three stand-ins for the young stars appeared on an outside set in the early hours of yesterday, it was hard to imagine getting them muggled, er, muddled up with the real thing.
The dismal doppelgangers were shooting in London's Piccadilly Circus for the two-part series finale, Harry Potter And The Deathly Hallows.
Stand-ins: A rotter of a Potter, a stranger Granger and a measly Weasley
Magic: Harry Potter's real stars Daniel Radcliffe, Emma Watson and Rupert Grint
The cast and crew have spent several days on location in Piccadilly Circus late at night filming what fans will recognise as the 'cafe attack' scene.
The scene takes place after the trio of friends flee the wedding of Ron's older brother Bill Weasley to Fleur Delacourt after finding out that Rufus Scrimgeour is dead and the Ministry of Magic is now under Voldemort's control.
They manage to fight off an attack from the two villains, but continue to flee to Harry's London hideout 12 Grimmauld Place.
Watch out for that bus: The trio realise a bus is heading straight for them
Near miss: They manage to jump back on to the kerb just in time
With the boys dressed in suits and Hermione in a stunning red dress, the pair arrive at a Muggle cafe, where they believe they are safe until they spot two Death Eaters.
The scene in the book originally takes place in Tottenham Court Road, but producers may have relocated it to Piccadilly Circus to give it a more scenic backdrop.
In between takes, the three young actors were spotted yawning and sipping on coffee in a bid to stay awake during the late night shoot.
Tiring: The young cast have been putting in long days filming the movie for the last two months
The Deathly Hallows, JK Rowling's last book in her best-selling series, will be split into two parts for the big-screen adaptation.
The cast and crew started filming the first part in February.
Part I is due for release in 2010, with Part II out in 2011. The prequel, Harry Potter And The Half-Blood Prince, will be released in the UK on 15 July.
It was originally scheduled for release last November, but was delayed so Warner Bros studio had a guaranteed 'major summer blockbuster' after the Hollywood writers' strike delayed a lot of movies.