Wachtell, Lipton, Rosen & Katz has tapped a former federal judge to defend it in the latest round of its malpractice battle with a company controlled by Carl Icahn. On Thursday John Gleeson, a prominent U.S. district judge in the Eastern District of New York who left the bench to join Debevoise & Plimpton earlier this year, appeared before a New York appellate court to defend a lower court’s rejection of the malpractice claims.

In 2013 Icahn-controlled CVR Energy Inc. sued Wachtell and partners Benjamin Roth and Andrew Brownstein in federal court for malpractice, claiming that they failed to explain the terms of the company’s fee agreement with two investment banks that CVR hired in an unsuccessful attempt to fend off Icahn’s takeover bid. The company wants Wachtell to reimburse it for the $36 million it paid the banks, as well as for Wachtell’s $6 million fee.