As a rule of thumb, you don’t want to go to Detroit and mess up the lyrics of beloved homegrown rapper Eminem to a crowd of thousands.

But that’s exactly what pop star extraordinaire Justin Bieber did on Sunday while throwing down a tribute to Slim Shady at Joe Louis Arena.

Bieber, a much bigger rap fan than many people know, treated his rabid fans to a verse from Eminem’s Oscar-winning track Lose Yourself but flubbed the very first line.

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Whoops: Justin Bieber flubbed the first line of Eminem’s Lose Yourself during a performance in Detroit, Michigan on Sunday night

‘His palms are heavy, knees weak, arms are heavy,’ Bieber rapped, whiffing on the correct ‘palms are sweaty’ line from the original tune.

The crowd must’ve either missed it or let it go as an easy mistake, however, as the usual cheering and screaming continued without pause.

It probably helped that Bieber didn’t miss a beat, cooly trotting across the stage as he wrapped up his homage to Eminem.

Fashion star: Justin donned a denim vest, black fedora and sharp red fingerless gloves for the show

This isn’t the first time that the singer has performed a verse from Lose Yourself live.

It’s become a bit of a ritual on Detroit visits, as he dropped the track in 2009 and 2010.

Bieber also dodged bigger trouble on Sunday, as border authorities found a small amount of marijuana and drug paraphernalia on one of the star’s tour buses as it was entering the U.S. from Ontario into Detroit.

No matter: The crowd didn’t seem to notice Bieber’s mistake on ‘Lose Yourself,’ which he’s performed in Detroit before

The authorities were alerted when a drug-sniffing dog picked up a suspicious scent as the bus was crossing the Ambassador Bridge, according to the Detroit Free Press.

Bieber was not on the vehicle and only the bus driver was cited.

The bus then entered the United States without any other problem – surely a relief for the busy pop star.

Gettin’ hot in here: Bieber reportedly gave the shirt off his back to a fan while with his entourage in New York City on Monday

Legendary: Eminem performs onstage at the 2011 Grammy Awards, held at the Staples Center in Los Angeles on Feb. 13, 2011