Led Zeppelin's classic 1971 song "Stairway to Heaven" is heading back to court.

A U.S. appeals court has ordered a new trial regarding copyright issues with the song that stem from a 2016 case in which the band was accused of copying the opening acoustic riff for its famous album track from Spirit's 1968 song "Taurus," which was included on their self-titled debut.

Even though Led Zeppelin were found not guilty, USA Today reports that a three-judge panel of the 9th U.S. Circuit Court of Appeals has unanimously ruled that "the lower court judge provided erroneous jury instructions" and sent the case back to court for another trial.

In 2015, a trustee for the estate of Spirit's late guitar player and "Taurus" composer, Randy California, filed a lawsuit against Led Zeppelin, charging them with stealing the opening riff heard in "Stairway to Heaven" from the Spirit song, which was released three years earlier. (California died in 1997.)

A five-day trial two years ago included Zeppelin's guitarist Jimmy Page and singer Robert Plant, who are credited with writing "Stairway to Heaven," testifying that their song was an original number.

Jurors agreed, noting that California owned the copyright to "Taurus" and Page and Plant had heard Spirit's song in the late '60s. Still, the jury claimed "there was no substantial similarity in the extrinsic elements" between the songs.

This new development puts a wrinkle in Led Zeppelin's otherwise celebratory 50th anniversary year, which so far has yielded a couple of remastered live albums, a new photo book and, just yesterday, the release of three new digital collections: a 30-track compilation, a 10-track Introduction to Led Zeppelin and the non-vinyl debut of the two previously unreleased song mixes that came out on Record Store Day earlier this year.