A California trial judge has cleared the way for a landmark malpractice lawsuit against Katten Muchin Rosenman, rejecting a defense request to apply a Washington, D.C., law that could have gutted the plaintiff’s claims for nearly $1 billion in damages.

The order Friday from Orange County Superior Court Judge William D. Claster reverses a June 10 tentative ruling in Katten’s favor, with the judge saying he initially “failed to correctly analyze where the alleged wrongful conduct occurred and then apply the governmental interest test in light of that revised analysis.”