Katy Perry, her collaborators and her record label must pay more than $2.78 million (£2.3 million) in damages after a jury decided her 2013 hit Dark Horse copied a Christian rap song.
It was a victory for rapper Marcus Gray, a relatively obscure artist once known as Flame, who lodged their copyright lawsuit five year ago.
In the time since legal proceedings started, they have faced constant court challenges and a trial against top-flight lawyers for Katy and the five other music-industry heavyweights who wrote the song.
The amount was less than the $20 million (£16.5 million) sought by lawyers for Marcus and his two co-writers on the 2009 song Joyful Noise, but they said they were pleased with the decision.
His lawyer, Michael A Kahn, told the jury: “These defendants have made millions and millions of dollars from their infringement of the plaintiff’s copyright.”
Katy herself was hit for just over $550,000 (£457,000), with label Capitol Records responsible for the vast majority of the money. Her lawyer, Christine Lepera, said they planned to vigorously fight the decision.
“The writers of Dark Horse consider this a travesty of justice,” she said.
Both sides agree that Katy herself made a profit of $2.4m (£2 million) from the song, while Marcus’s lawyers argued that it grossed about $41m (£34m).
The pop star testified at the beginning of the trial but has not been in court since.
Because the rhythmic instrumental riff from Joyful Noise plays through 45% of Dark Horse, Kahn said his clients were entitled to 45% of the entire earnings of Katy’s album Prism, where her song appears.
The defence recommended dividing the award money by the number of songs on the album.
“A CD is a CD, you can’t break it into pieces,” Kahn said. “Every album had an infringing song. And not just any song, but the most popular song on the album.”
Lawyers for Katy and her co-defendants, which included Capitol Records and producer Dr Luke, said the millions Marcus sought were based on ludicrous figures.
“They’re not seeking fairness,” the defendants’ lawyer Aaron M Wais told the jury. “They’re seeking to obtain as much money as possible.”
Recent years have brought similar wins in disputes over hit songs, though usually with big pop stars on both sides.
In the case of another 2013 mega-hit, Blurred Lines, a jury found singers Robin Thicke and Pharrell Williams copied R&B legend Marvin Gaye’s Got to Give it Up.
Robin and Pharrell were initially ordered to pay Marvin’s estate nearly $7.4m (£6m). The award was trimmed last year to just short of $5m (£4.1m) on appeal.
No fight was required in 2016 when Tom Petty won a piece of British soul singer Sam Smith’s hit Stay With Me. Tom’s publishers said that while it was likely coincidental, the song’s melody closely resembled his 1989 song I Won’t Back Down.
Tom and Jeff Lynne were added as co-writers on Smith’s song, but details on a settlement figure were not released.