The district court ruled California’s statutory scheme for providing work credits to convicted murderers violates the equal protection clause. Brodheim v. Rowland, 783 F.Supp. 1245 (N.D.Cal. 1991). The court’s interpretation of California law was expressly repudiated by In re Singer, 13 Cal.App.4th 1755, 17 Cal.Rptr.2d 395 (6th Dist. 1993). “We are bound by that state court’s construction of its own penal statute,” McSherry v. Block, 880 F.2d 1049, 1052 (9th Cir. 1989), and may re-examine a state court’s interpretation of its own law only if “the court’s interpretation is untenable or amounts to a subterfuge to avoid federal review of a constitutional violation.” Taylor v. Kincheloe, 920 F.2d 599, 609 (9th Cir. 1990) (citations and internal quotation marks omitted); see also Ward v. Love County, 253 U.S. 17, 22, 40 S.Ct. 419, 421, 64 L.Ed. 751 (1920). Singers interpretation of California law is straightforward and reasonable. There is no evidence of subterfuge.

Brodheim challenges the district court’s ruling that he has no due process right to continue earning one-for-one work credits under Cal.Penal Code § 2933. See 783 F.Supp. at 1248. Brodheim has already received credit for his work prior to In re Monigold, 205 Cal.App.3d 1224, 253 Cal. Rptr. 120 (4th Dist. 1988) (holding § 2933 credits are not available to convicted murderers, but that murderers must receive credit for all work prior to court’s decision). Section 2933 does not create a liberty interest in work credits for inmates who have not engaged in any work that would entitle them to such credits. Toussaint v. McCarthy, 801 F.2d 1080, 1095 (9th Cir. 1986). Being ineligible for the program under state law, Brodheim has no due process right to continue earning credits under § 2933. Olim v. Wakinekona, 461 U.S. 238, 250, 103 S.Ct. 1741, 1748, 75 L.Ed.2d 813 (1983) (there is no due process violation if there is no liberty interest to protect).

We affirm the district court’s denial of Brodheim’s due process claim, but vacate the judgment of the district court with respect to Brodheim’s equal protection claim. We remand for further proceedings consistent with this order and with Singer, including consideration of the additional equal protection *718 claims raised by Brodheim but not addressed by the district court.