The Ron Howard film, based on a series of interviews US president Richard Nixon gave to the talkshow host in 1977, has changed some details of what really happened.
"I voluntarily gave up my rights to editorial control of it. I'm not complaining but it does mean that 10 to 15% of the film is fiction," he said.
He added that actual events were slightly inaccurate in the original production, which he puts down to the writer attempting to create a more audience-friendly narrative.
"I think Peter [Morgan, the playwright] did it this way to make me out to be the underdog, more a showman than a journalist," said Frost.