Led Zeppelin will face a new trial over whether it stole the opening guitar riff for its 1971 anthem 'Stairway to Heaven'.
Last week, a United States Court of Appeals threw out a 2016 verdict in the rock band's favor, citing a series of errors by the trial judge.
The new decision revives one of the music industry's most closely-watched copyright cases, potentially exposing Led Zeppelin lead singer Robert Plant and guitarist Jimmy Page to millions of dollars in damages.
Lawyers for the defendants had no immediate comment.
The lawsuit was filed by Michael Skidmore, a trustee for the songs of Randy Wolfe, a guitarist for the band Spirit.
Mr Skidmore accused Mr Plant, 70, and Mr Page, 74, of stealing the iconic opening to song from one by the band Spirit. The obscure instrumental track, 'Taurus', was written four years before the famous Led Zeppelin song.
Mr Skidmore said the songs had similar chord progressions and that Mr Page may have written 'Stairway to Heaven' after hearing 'Taurus', while Led Zeppelin and Spirit were touring together.
Mr Wolfe, who performed as Randy California, had complained in interviews about the songs' similarities, but did not sue prior to his death by drowning in 1997.
Jurors determined that while Mr Plant and Mr Page, who testified at the trial, had access to 'Taurus', the song's riff was not intrinsically similar to the opening of 'Stairway to Heaven'.
But in this week's decision, Circuit Judge Richard Paez said the trial judge erred in failing to instruct jurors that the trustee could prevail if Mr Wolfe had created a "sufficiently original combination" of otherwise unprotectable music elements.
Judge Paez also said the previous judge erred in instructing jurors about the copyrighting of music elements in the public domain, and should have let them listen to Taurus while Page testified, to assess his demeanor and help determine whether he had access.
"We do not dispute that Led Zeppelin is one of the greatest bands in history, but their plagiarism indelibly stains their legacy," Mr Skidmore's lawyer, Francis Malofiy, said in an email.
The case was returned to US District Judge Gary Klausner in Los Angeles.
This week's decision followed a March copyright ruling by another appeal court panel upholding a $5.3 million judgment to Marvin Gaye's children. They accused Robin Thicke and Pharrell Williams of creating the 2013 smash 'Blurred Lines' by copying Gaye's 1977 song 'Got to Give It Up'.