The U.S. Court of Appeals for the Federal Circuit gave new impetus Wednesday to a 15-year battle between Atlanta-based soft drink giant The Coca-Cola Co. and longtime rivals Royal Crown Cola Co. and Dr Pepper/Seven Up Inc. over Coke’s efforts to trademark the word “Zero” for exclusive use on its no-calorie sports and soft drinks.

The circuit court dealt a setback to Coke when it vacated and remanded the trademark case to the U.S. Patent and Trademark Office’s Trademark Trial and Appeal Board. The three-judge panel ruled the board applied the incorrect legal standard when it decided in 2016 that Coke could trademark “Zero” for more than a dozen no-calorie soft drinks and sport drinks.