O’Melveny & Myers scored a big win for Warner Brothers Entertainment Inc. on Thursday in the company’s ugly copyright battle with the heirs to the creators of Superman.

In a 6-page ruling, the U.S. Court of Appeals for the Ninth Circuit ruled that the heirs of Superman co-creator Jerry Siegel signed away their rights to the Man of Steel in a 2001 agreement with Warner Brothers. The Siegel family, represented by Hollywood attorney Marc Toberoff, had argued that the 2001 deal wasn’t binding. The Ninth Circuit rejected that argument, noting that Siegel’s then-lawyer called the agreement a “monumental accord.” The ruling deals the Siegels a major blow in their decades-long bid to increase their share of the Superman profits.