The film's director/star cast the Persian actors who appear in the drama on the basis they could speak Farsi - but when one came to shoot his speaking part it quickly became clear he could only act like he knew the language.
The movie star insisted on authentic Farsi for tense scenes in the film, which is set in Iran during the country's revolution in 1979 and 1980.
He tells The Hollywood Reporter, ""This movie was the only time I really fired people, but I had to do it. I had all these Persian actors who were supposed to speak Farsi. And often they would audition in English and I would say, 'You can speak Farsi, right?' 'Oh, yes, yes.'
""A guy came in for a really crucial part, and on the day of shooting, we were blocking the scene, and this guy's got this mini speech. And the guy did it, and it was just terrible. He was sort of like, you know, twisting the moustache and being the (stereotypical) Iranian villain and having the accent and adding all these flourishes.
""A couple (of) times I said, 'Just do nothing and say your lines. Let's try that.' And just previous to that, there was this guy who had a little bit in the movie. But it was so nice. And then when this other guy was blowing it - and not just blowing it, but hamming it up - it made it easy to say, 'No, you know, you're trying to ruin my movie'.""
But Affleck hopes it's the one and only time he'll have to fire an actor - because he remembers how it felt to fear being axed from a movie early in his career.
He adds, ""It's the worst thing in the world because I know, as an actor, what it's like. I was a child actor, and the director threatened to fire me. That traumatised me. I was 13 years old. And I went around in fear of being fired.""