People can now sing the song Happy Birthday To You in public without fearing that they will have to pay royalties.
A judge in the United States has ruled Warner/Chappell Music Inc no longer owns the copyright on the iconic song.
The music publisher had previously collected royalties on the track after buying the firm that owned the copyright in 1988.
The song's lyrics were first written down in 1911 and the music and words were first published together in 1935.
Under US law, copyright remains on a piece of music for 95 years after it is first published.
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It states anyone performing a piece of music within copyright who is deemed to have an audience, has to pay the publisher.
Warner/Chappell's hold on the copyright was challenged by a documentary maker who was making a film about the history of the song.
Good Morning To You Productions Corp claimed that the track was "dedicated to public use and in the public domain."
US District Judge George H King has now decided that the song's original copyright, obtained by the Clayton F Summy Co from the song's writers, only covered the tune's musical arrangement and not the lyrics.
The song's original score was accompanied by a different set of lyrics, penned by sisters Mildred Hill and Patty Hill sometime before 1893.
That song, which used the same melody, was called Good Morning To All.
"The origins of the lyrics to Happy Birthday (the Happy Birthday lyrics) are less clear," the judge said in his 43-page ruling.
"Because Summy Co never acquired the rights to the Happy Birthday lyrics, defendants, as Summy Co's purported successors-in-interest, do not own a valid copyright in the Happy Birthday lyrics," Judge King concluded.
Warner/Chappell said it was looking at the court's opinion and considering its options.
Some musicians praised the ruling.
Ruypa Marya, who had to pay Warner/Chappell $455 to include Happy Birthday To You on a live album, said: "I hope we can start reimagining copyright law to do what it's supposed to do - protect the creations of people who make stuff so that we can continue to make more stuff."
According to Guinness World Records, Happy Birthday To You has the most famous lyrics of any song in the English language.
The song is also sung in numerous other languages around the world.