Appellant, Andrew Holguin, appeals the district court’s denial of his petition for habeas corpus under 28 U.S.C. § 2254. He contends that the district court erred in concluding that the Arizona Department of Correction’s change in its method of calculating parole eligibility on consecutively imposed sentences, which applied retroactively to his detriment, did not violate the prohibition against ex post facto laws contained in the United States Constitution. We affirm.
I.
On July 8, 1972, Holguin began serving three concurrent ten to twenty year sentences after conviction on three counts of assault with a deadly weapon. On February 28,1973, Holguin received an additional sentence of nine to ten years for kidnapping to run consecutively with his earlier sentences for assault.
At the time of sentencing on both counts, the Arizona statute governing eligibility for parole provided:
Every [pjrisoner who has served one-third of the minimum sentence, computed without any time deductions credited, if he has served more than one calendar year, shall be given an opportunity to appear before the board and apply for releases upon parole.
Ariz.Rev.Stát. § 31-411(A)(1). The Arizona Department of Corrections, relying on a 1973 unpublished opinion of the Arizona Attorney General, determined parole eligibility for consecutive sentences by taking one-third of the total minimum terms of *373imprisonment — adding the consecutive sentences together as if they were one continuous sentence. Using that approach, the Board calculated that Holguin would be eligible for parole on November 8, 1979.
In 1974, however, the Arizona Supreme Court, in Mileham v. Arizona Board of Pardons and Prisons, 110 Ariz. 470, 520 P.2d 840 (1974), interpreted section 31-A11(A)(1) to hold that a prisoner serving a sentence for escape made consecutive to a robbery sentence became eligible for parole only after serving the complete sentence on the robbery conviction and one-third of the escape sentence. Subsequently, the Arizona Attorney General issued a new opinion, consistent with Mileham, that any prisoner sentenced to consecutive sentences would have to complete the first sentence and one-third of the second before being eligible for parole. Under this new approach, Holguin would have been eligible for consideration for parole on September 9, 1985.
In 1978, the Arizona legislature, responding to Mileham, amended the parole statute to provide that a person convicted of a crime committed prior to October 1, 1978, could be paroled from his sentence under that conviction to begin serving a second consecutive sentence. See 1978 Ariz.Sess. Laws ch. 164 § 30(B). Pursuant to this amendment, Holguin was paroled in November, 1980, from his first sentence to his nine to ten year consecutive sentence.1 He thus would become eligible for parole on the consecutive sentence on November 4, 1983, some five years after the initial parole eligibility date.
After exhausting his State remedies, Holguin filed this federal habeas petition, claiming that the changes wrought by the Attorney General’s new opinion and the subsequent legislative amendments violated the ex post facto clause of the United States Constitution. The district court dismissed the petition, concluding that the Attorney General’s subsequent opinion was merely “a corrected interpretation of a state statute” based on the Arizona Supreme Court’s decision in Mileham and therefore did not constitute an ex post facto enactment.2
II.
The ex post facto provision of Article I, section 10 of the United States Constitution forbids the states from passing any law “which punishes as a crime an act previously committed which was innocent when done; or imposes additional punishment to that then prescribed.” Weaver v. Graham, 450 U.S. 24, 28, 101 S.Ct. 960, 964, 67 L.Ed.2d 17 (1981) (quoting Cummings v. Missouri, 71 U.S. (4 Wall.) 325-26, 18 L.Ed. 356 (1867). See also Beazell v. Ohio, 269 U.S. 167, 169-70, 46 S.Ct. 68, 68-69, 70 L.Ed. 216 (1925); Knapp v. Cardwell, 667 F.2d 1253, 1262 (9th Cir.1981). The purpose of the prohibition is to provide fair warning of legislative statutes and to prevent arbitrary and oppressive legislation. Weaver, 450 U.S. at 28, 101 S.Ct. at 964; Dobbert v. Florida, 432 U.S. 282, 293, 97 S.Ct. 2290, 2298, 53 L.Ed.2d 344 (1977).
In Weaver v. Graham, the Supreme Court held that a Florida statute which reduced the availability of gain time for good behavior in prison constituted an ex post facto law when applied to a prisoner who was convicted for a crime committed before the statute’s enactment. The Court concluded that although the gain time provision was not technically part of the petitioner’s sentence, it “substantially alter[ed] the consequences attached to a crime already completed.” 450 U.S. at 33, 101 S.Ct. at 966.
*374Holguin, relying on Weaver, argues that the Arizona Attorney General’s change in its opinion regarding computation of parole eligibility, upon which the Department of Corrections relied in setting its policy, violated the ex post facto clause since it increased the minimum amount of time he would have to serve before being eligible for parole. In particular, Holguin points to this court’s opinion in Love v. Fitzharris, 460 F.2d 382 (9th Cir.1972), vacated as moot, 409 U.S. 1100, 93 S.Ct. 896, 34 L.Ed.2d 682 (1973). In Love the California Department of Corrections changed its interpretation of the California parole statute to increase the minimum term for prisoners serving consecutive sentences prior to eligibility for parole. The court found that the change violated the ex post facto provision, concluding that the ex post facto prohibition applies to retroactive administrative interpretations as well as legislative enactments.
Yet appellant’s argument ignores the impact of the Arizona Supreme Court’s decision in Mileham v. Arizona Board of Pardons and Paroles, 110 Ariz. 470, 520 P.2d 840 (1974). If, as the district court concluded, the result in Mileham required that the Attorney General change what had been an incorrect opinion regarding parole for consecutive sentences, then the ex post facto issue here is controlled by this court’s opinion in Mileham v. Simmons, 588 F.2d 1279 (9th Cir.1979).
In Mileham v. Simmons, this court specifically held that the retroactive application of the Arizona Supreme Court’s opinion in Mileham v. Arizona Board of Pardons and Paroles to recalculate parole eligibility did not violate ex post facto principles. To the extent that that rationale applies here, we are bound by our own rules. We distinguished between a change in an administrative interpretation of state law made by the agency itself, such as that found in Love v. Fitzharris, and a court decision authoritatively construing state law. In the latter case, we noted, the ex post facto clause by its own terms does not apply. 588 F.2d at 1280. See Marks v. United States, 430 U.S. 188, 191, 97 S.Ct. 990, 992, 51 L.Ed.2d 260 (1977). Nevertheless, we recognized that the principle of fair warning implicit in the ex post facto prohibition requires that judicial decisions interpreting existing law must have been foreseeable. Id. See Marks, 430 U.S. at 191-92, 97 S.Ct. at 992-993; Bouie v. City of Columbia, 378 U.S. 347, 354, 84 S.Ct. 1697, 1703, 12 L.Ed.2d 894 (1964); Forman v. Wolff, 590 F.2d 283, 285 (9th Cir. 1978) cert. denied, 442 U.S. 918, 99 S.Ct. 2839, 61 L.Ed.2d 285 (1979). The Mileham v. Simmons court concluded that the Arizona Supreme Court’s decision satisfied the foreseeability requirement and therefore did not deprive that petitioner of fair warning. Id.3
The outcome of Holguin’s case therefore turns on whether the changed Arizona Attorney General’s opinion was merely a reflection of the Arizona Supreme Court’s correcting statutory holding in Mileham, or whether it was an extension of Mileham. That in turn depends upon whether the Arizona court’s Mileham opinion is limited to consecutive sentences imposed for escape convictions or applies generally to consecutive sentences. We conclude that the general interpretation is the correct analysis of the Arizona Supreme Court’s holding.
From the beginning, the Arizona Supreme Court’s opinion in Mileham treats sentences for escape convictions as part of *375the larger category of consecutive sentences in general. Thus the Court states:
Undoubtedly, the Legislature intended to increase the punishment of those who attempted to or escaped from the State Prison and, therefore the punishment for a violation of the escape statute is a sentence consecutive to the sentence or sentences the escapee was serving at the time of his escape or attempt.... When consecutive sentences are imposed, the subsequent sentence commences at the expiration of the prior sentence or sentences.
520 P.2d at 842. The Court then resolves the issue before it by looking to the applicability of the parole statute to consecutive sentences in general, concluding that since parole is “a service of the balance of the sentence outside the prison,” 520 P.2d at 843, and a consecutive sentence may only begin at the expiration of the first sentence, the Board of Corrections could not parole any prisoner to begin a consecutive sentence.
In sum, it is not possible to limit the Mileham holding to consecutive sentences for escape convictions because the Court resolved the issue by deciding the application of the parole statute for all consecutive sentences. Therefore the Arizona Attorney General’s opinion does no more than require the Department of Corrections to follow the dictates of Mileham. Under the circumstances, Holguin’s reliance, if any, on the Attorney General’s earlier erroneous interpretation of State law could not preclude the State court from judicially correcting that interpretation, Mileham v. Simmons, 588 F.2d at 1280,4 and therefore the Department of Corrections did not violate his constitutional rights in recalculating his parole eligibility.
Affirmed.
. Holguin became eligible for consideration for parole immediately upon the effective date of the new legislation, October 1, 1978. However, his first two requests for parole heard in November, 1978, and November, 1979, were denied.
. Since the district court concluded that the initial recalculation of Holguin’s parole eligibility survived ex post facto scrutiny it did not need to address whether the subsequent legislative amendments reducing the minimum term before Holguin was eligible for parole were ex post facto. See Dobbert v. Florida, 432 U.S. 282, 294, 97 S.Ct. 2290, 2298-2299, 53 L.Ed.2d 344 (1977) (“It is axiomatic that for a law to be ex post facto it must be more onerous than prior law.”)
. Holguin argues that the statement in Mile-ham that the petitioner “did not have a vested right in such an erroneous interpretation,” 588 F.2d at 1280, indicates that the court’s opinion is based on a “vested rights” analysis specifically disapproved by the Supreme Court in Weaver v. Graham, 450 U.S. at 30, 101 S.Ct. at 965 (“The presence or absence of an affirmative enforceable right is not relevant, however, to the ex post facto prohibition, which forbids the imposition of punishment more severe than the punishment assigned by law when the act to be punished occurred.”)
Yet aside from the single inadvertent reference stated, the Mileham opinion does not rely on the theory that the petitioner did not have a vested right to parole eligibility. Instead, as suggested, it is based on the distinction between administrative and judicial interpretations of state law and the foreseeable character of the Arizona Supreme Court’s decision in Mileham.
. We do not interpret certain language in the Supreme Court’s decision in Weaver v. Graham to mean, as Holguin suggests, that judicial decisions detrimentally affecting a prisoner’s length of imprisonment may only be applied prospectively, whether they are foreseeable or not.
In examining the reason that the ex post facto clause is applicable to good time provisions, the Court in Weaver refers to “a prisoner’s eligibility for reduced imprisonment” as a factor in both the defendant’s decision to plea bargain and the judge’s calculation of the sentence to impose. 450 U.S. at 32, 101 S.Ct. at 966.
However, as indicated, Weaver did not involve a judicial change in eligibility for reduced imprisonment. Nor is there any indication in the opinion that the Court intended that its earlier decisions regarding retroactive court decisions, upon which the court relied in Mile-ham, are inapplicable in the plea bargaining or sentencing context. Such an interpretation would suggest that a court could never retroactively correct a prior interpretation of state law advanced by a state agency, no matter how erroneous, if it affected the terms or length of imprisonment. We refuse to adopt such a rule.