The Federal Circuit Court of Appeals has decided not to restore Merck’s historic $2.5 billion patent win over Gilead in a hepatitis C drug dispute.

Merck and its subsidiary Idenix Pharmaceuticals sued Gilead in 2013 alleging that its hepatitis C treatments Sovaldi and Harvoni infringed on a patent Idenix had for treating hepatitis C. The case went to trial in December 2016 and a jury ruled in Merck’s favor, awarding the drugmaker $2.5 billion — the largest patent award ever. A federal judge threw out the verdict in 2018 finding that the patent was invalid.

The Federal Circuit Court of Appeals has upheld the judge’s ruling, agreeing that the patent was invalid for “lack of written description” of how the invention worked.