Cumberbatch plays Assange in The Fifth Estate, an upcoming movie based on the WikiLeaks saga, which left the website's founder living in sanctuary at the Ecuador embassy in London as he fights extradition to Sweden.
But Assange is unimpressed with Cumberbatch's performance in the film, branding the actor's attempts at an Australian accent "grating".
He tells the Sydney Daily Telegraph, "We're all used to foreign actors trying to do Australian accents and it's so grating on the ear... When you hear a Brit trying to do an Australian accent and your own accent, I can't tell you how grating it is."
Assange is wanted in the U.S. after publishing thousands of classified military documents on his website.