Bostonian Customs Agent to Joel Edgerton: 'Don't F--k Up' Accent in 'Black Mass'

·Senior Correspondent, Yahoo Entertainment

Joel Edgerton realized the importance of getting the accent right as he made his way into the U.S. from Canada to film the new gangster thriller, Black Mass. And it came in the form a stiff warning from a U.S. customs agent.

“He was from South Boston and he knew that I was doing this movie,” Edgerton, who plays corrupt FBI agent John Connolly, told Yahoo Movies. “And he literally said to me, he’s like, ‘You better get it right. Don’t f–k it up.’ He said the words to me, 'Don’t f–k it up.’”

Black Mass, which tells the story of crime boss James 'Whitey’ Bulger (Johnny Depp), who ruled the streets of South Boston through much of the 1970s and '80s, is an ensemble brimming with excellent performances and spot-on “Southie” accents. Asked what they did to master the brogues in Mass, the cast’s answers ranged from obvious to fear-inducing.

Related: From Whitey Bulger to Willy Wonka, the Secrets Behind Johnny Depp’s Movie Transformations

“Be born there, grow up there,” said Julianne Nicholson, who grew up in the city’s suburb of Medford, Massachusetts. “Being around people from Boston,” added Peter Sarsgaard, who plays slimy Bulger associate Brian Halloran. “If we had been shooting it Spain it would’ve been a lot more difficult.”

Edgerton’s secret? “Terror,” said the 41-year-old Aussie actor sporting a new short reddish blond 'do for his upcoming 1950s-set drama Loving. “Fear of being chased down by every Bostonian.”

Or not even being allowed into the country.

Black Mass is now in theaters. Watch the trailer: