What is the test for determining whether a judgment is valid under Rule of Civil Procedure 60(b)(4)?

We review de novo the district court's decision to set aside its 1986 judgment as void under Federal Rule of Civil Procedure 60(b)(4) because "the question of the validity of a judgment is a legal one." Retail Clerks Union Joint Pension Trust v. Freedom Food Center, 938 F.2d 136, 137 (9th Cir.1991). ¹ We also review de novo the district court's summary judgment. Kruso v. International Tel. & Tel. Corp., 872 F.2d 1416, 1421 (9th Cir.1989), cert. denied, 496 U.S. 937, 110 S.Ct. 3217, 110 L.Ed.2d 664 (1990).