Katy Perry has lost a copyright lawsuit. Picture: AP
Katy Perry has lost a copyright lawsuit for her 2013 hit "Dark Horse", as a jury ruled she had copied the Christian rap song "Joyful Noise".

The 34-year-old pop superstar and her collaborators including, Juicy J - who had a rap verse on the song - and producer Dr Luke were accused of ripping off the melody from Marcus 'Flame' Gray and Chike-Ojukwu's 2009 song "Joyful Noise" five years ago, and on Monday a Los Angeles court ruled in their favour.

Katy's lawyer, Christine Leperad, had argued that the pair were trying to claim copyright for basic elements of the song. 

She told the courtroom: "They're trying to own basic building blocks of music, the alphabet of music that should be available to everyone."

The "Teenage Dream" singer and the team behind the song - which had six co-writers - testified that they had never heard of "Joyful Noise" or their Christian music before.

However, Grey's legal representation, Michael Khan, insisted: "They're trying to shove Mr Gray into some gospel music alleyway that no one ever visits."

It was also noted that Katy - who is engaged to actor Orlando Bloom - started her career in church and playing gospel music.

During the trial, the song was meant to be played to the court but the speakers failed, and Katy lightened the tone when she offered to perform the song.

It will be determined how much Katy and her collaborators will have to pay Gray in damages for copyright infringement.

"Dark Horse" was released on Katy's 2013 LP "Prism" and has sold over 13 million copies worldwide.