In an a-peel of a case that could have slippery implications, a federal court ruled on Thursday that a banana costume may be protected by copyright law.

A full-body banana costume sold by the Arizona product manufacturer Kangaroo Manufacturing Inc may be too similar to one originally sold by the New Jersey costumer Rasta Imposta, the district judge Mitchell S Goldberg of the eastern district of Pennsylvania said in an opinion.

“Because Rasta established a reasonable likelihood that it could prove entitlement to protection for the veritable fruits of its intellectual labor,” he said, “we will affirm.”

Rasta Imposta had a partnership with Kangaroo Manufacturing (until their business went rotten) and registered a copyright of a banana costume in 2010. After the two split, Kangaroo began to sell a similar style of costume, and Rasta sued the company in October of 2017 for copyright infringement, trade dress infringement and unfair competition.

Costumes generally cannot be copyrighted, said Mickie A Piatt, an associate professor at Chicago-Kent College of Law who focuses on intellectual property law – but it’s complicated.

“If you can conceptually separate banana-ness from costume-ness, then the banana may be copyrightable,” she said. “If I sculpted a banana, I could copyright it, but if it’s simply a costume, I cannot.”

Costumes generally cannot be copyrighted, but a judge ruled a banana costume may be protected by copyright law. Photograph: Silvertop Associates, Inc v Kangaroo Manufacturing

In other words, functional features of a costume like creating holes for arms and a head cannot be copyrighted, but the material and design may be. Initially, a district court ruled in favor of Kangaroo, saying the costume performs a “solely utilitarian function”.

But in the ruling on Thursday, the judge countered this, saying “we must imagine the banana apart from the useful article.” He cited the 2017 supreme court decision that found a cheerleader uniform was copyrightable, noting that while utilitarian functions of the banana costume cannot be copyrighted, creative aspects can.

“Those sculptural features include the banana’s combination of colors, lines, shape and length,” he said. “Copyrighting Rasta’s banana costume would not effectively monopolize the underlying idea because there are many other ways to make a costume resemble a banana.”

Rasta provided 20 examples of banana costumes that would not infringe on its copyright, and the court noted these were distinguishable from the original design “based on the shape, curvature, tips, tips’ color, overall color, length, width, lining, texture and material”.

“Although a banana costume is likely to be yellow, it could be any shade of yellow – or green or brown for that matter,” the opinion said. “Although a banana costume is likely to be curved, it need not be – let alone in any particular manner.”

Lori Andrews, a professor of law at Chicago-Kent College of Law, said the decision could create a dangerous precedent, making it difficult for people in the creative field to sell their work without being legally challenged.

“Now copyright law is getting out of hand,” she said. “If a simple banana costume can be found to infringe another banana costume, what’s to prevent someone from copyrighting the plot boy meets girl and forbidding anyone else from writing a book in which a boy meets a girl?”