OPINION
Robert M. Thomas seeks a writ of habeas corpus under 28 U.S.C. § 2254 because *170of the denial of his parole by the Pennsylvania Board of Probation and Parole (the “Board”).1 At the time of the Board’s decision in 2004, it was operating under Pennsylvania’s recently amended Parole Act (the “Act”). Act of Dec. 18,1996, 1996 P.L. 1098, No. 164, § 1 (codified at 61 Pa. Cons.Stat. § 331.1). The amendments had the effect of placing more weight on considerations of public safety than was previously the case in the Board’s parole decisions. See Mickens-Thomas v. Vaughn, 321 F.3d 374, 385-86 (3d Cir.2003). This, of course, had the potential to make it more difficult for state prisoners to be granted parole. As a result, Pennsylvania’s retroactive application of the new standard to prisoners sentenced before the Act had taken effect raised ex post facto concerns. See U.S. CONST, art. I, § 10, cl. 1.
Prior to the denial of parole that is challenged here, Thomas similarly had been denied parole in 2001. Raising the same ex post facto concerns as in this petition, he filed for mandamus review of the former denial and pursued that claim through the Pennsylvania court system to the Pennsylvania Supreme Court. That Court reserved decision in Thomas’s case until it issued an opinion in Finnegan v. Pa. Bd. of Probation & Parole, 576 Pa. 59, 838 A.2d 684 (2003). Finnegan resolved for the Pennsylvania courts — temporarily, as it turned out — the questions that had been swirling about the Act and its effect on parole determinations. The Court ruled that the Ex Post Facto Clause was not violated by the Act’s retroactive application. Id. at 690.2
It was in the face of Finnegan that Thomas filed in federal court the petition that is the subject of this appeal. As did his Pennsylvania mandamus case, which challenged the first denial of his parole, Thomas’s habeas petition here challenges the second denial of his parole on ex post facto grounds. For federal courts to rule on petitions challenging state custody, petitioners generally must have exhausted all state-law remedies. 28 U.S.C. § 2254(b), (c); Doctor v. Walters, 96 F.3d 675, 681 (3d Cir.1996). Thomas readily admits that he has not pursued a challenge to his second denial of parole in the Pennsylvania courts, but asserts that the doctrine of futility excuses his failure to exhaust. See Whitney v. Horn, 280 F.3d 240, 252 (3d Cir. 2002); Toulson v. Beyer, 987 F.2d 984, 987 (3d Cir.1993).3 His reasoning is that because the Pennsylvania Supreme Court in Finnegan had recently rejected an ex post facto challenge to the Act (indeed, it had reserved decision on Thomas’s own earlier challenge pending its decision in Finnegan), it would have been futile for him to raise the same claim to the same Court so soon.
Our Court’s decision in Parker v. Kelchner, 429 F.3d 58 (3d Cir.2005), issued after Thomas filed this petition, forecloses his argument. In Parker, “we agree[d] with our sister Circuits ... that likely futility on the merits does not excuse a failure to exhaust a claim in state court.” *171Id. at 63. “Allowing petitioners to bypass state court merely because they believe that their constitutional claims would have failed there on the merits would fly in the face of comity and would deprive state courts of [a] critical opportunity to examine and refine their constitutional jurisprudence.” Id. at 64 (citing Engle v. Isaac, 456 U.S. 107, 128, 102 S.Ct. 1558, 71 L.Ed.2d 783 (1982)). As Parker noted, see 429 F.3d at 64 n. 5, the Pennsylvania Supreme Court eventually overruled Finnegan with its decision in Cimaszewski v. Bd. of Probation & Parole, 582 Pa. 27, 868 A.2d 416, 426-27 (2005) (holding that “changes in the laws governing parole may violate the ex post facto clause.” (double emphasis in original)).4
Thomas has failed to exhaust his ex post facto claim in the Pennsylvania courts. We therefore will affirm the judgment of the District Court.