ROVNER, Circuit Judge,
concurring.
Defendants’ petition for rehearing raised one issue that, in my view, should have prompted the panel to further amend its March 25, 1996, opinion. The opinion suggests that the Rooker-Feldman doctrine bars Michael Gulmetti, as well as Ruth Westphal, from claiming that the district court lacked subject matter jurisdiction over the present case because the underlying Arizona judgment against Westphal was invalid. Yet, because he was not a party to the Arizona action, Rooker-Feldman would not preclude Gulmetti from advancing that argument. See, e.g., United States v. Owens, 54 F.3d 271, 274 (6th Cir.1995); Leaf v. Supreme Court of Wisconsin, 979 F.2d 589, 598 (7th Cir.1992), cert. denied, 508 U.S. 941, 113 S.Ct. 2417, 124 L.Ed.2d 639 (1993). The argument ultimately must fail, however, because the validity of the Arizona judgment does not affect our subject matter jurisdiction. To the extent Gulmetti may have been able to viably assert the invalidity of the Arizona judgment as a defense on the merits, he forfeited that argument when he abused the discovery process below. For these reasons, I concur in the denial of defendants’ petition for rehearing.