502us2$26D 01-22-99 08:32:58 PAGES OPINPGT 390 RUFO v. INMATES OF SUFFOLK COUNTY JAIL Opinion of the Court “would necessarily imply that the only legally enforceable obligation assumed by the state under the consent decree was that of ultimately achieving minimal constitutional prison standards. . . . Substantively, this would do violence to the obvious intention of the parties that the decretal obligations assumed by the state were not confined to meeting minimal constitutional requirements. Procedurally, it would make necessary, as this case illustrates, a constitutional decision every time an effort was made either to enforce or modify the decree by judicial action.” Plyler v. Evatt, 924 F. 2d 1321, 1327 (CA4 1991). While a decision that clarifies the law will not, in and of itself, provide a basis for modifying a decree, it could constitute a change in circumstances that would support modification if the parties had based their agreement on a misunderstanding of the governing law. For instance, in Pasadena City Bd. of Ed. v. Spangler, 427 U. S. 424, 437–438 (1976), we held that a modification should have been ordered when the parties had interpreted an ambiguous equitable decree in a manner contrary to the District Court’s ultimate interpretation and the District Court’s interpretation was contrary to intervening decisional law. And in Nelson v. Collins, 659 F. 2d 420, 428–429 (1981) (en banc), the Fourth Circuit vacated an equitable order that was based on the assumption that double bunking of prisoners was per se unconstitutional. Thus, if the sheriff and commissioner could establish on remand that the parties to the consent decree believed that single celling of pretrial detainees was mandated by the Constitution, this misunderstanding of the law could form a basis for modification. In this connection, we note again, see supra, at 375, that the decree itself recited that it “sets forth a program which is both constitutionally adequate and constitutionally required.” (Emphasis added.)