delivered the opinion of the court:
The question in this case is whether Public Act 88— 311, which excludes inmates from the opportunity to increase good-conduct credit, violates the ex post facto clauses of the Federal and Illinois Constitutions (U.S. Const., art. I, § 10; Ill. Const. 1970, art. I, § 16). We hold that it does.
BACKGROUND
As of September 10, 1990, section 3 — 6—3 of the Unified Code of Corrections applied a multiplier to increase the "day for a day” credit certain prisoners could earn toward early release. (Ill. Rev. Stat. 1991, ch. 38, par. 1003 — 6—3 (amended by Pub. Act 86 — 1373, eff. September 10, 1990).) Inmates engaged in Department of Corrections educational programs who met specified goals were eligible to receive credit increased by a factor of 1.25. (Ill. Rev. Stat. 1991, ch. 38, par. 1003 — 6—3.) The multiplier was not available for those convicted of first or second degree murder or those convicted of a Class X felony. (Ill. Rev. Stat. 1991, ch. 38, par. 1003— 6 — 3.) Nor was it available for inmates who were convicted of a felony while engaged in the programs. Ill. Rev. Stat. 1991, ch. 38, par. 1003 — 6—3.
Public Act 88 — 311, effective August 11, 1993, amended section 3 — 6—3. (Pub. Act 88 — 311, eff. August 11, 1993 (amending Ill. Rev. Stat. 1991, ch. 38, par. 1003 — 6—3).) Among the changes, the act precluded application of the multiplier to categories of inmates previously eligible for it under section 3 — 6—3. (Pub. Act 88 — 311, eff. August 11, 1993 (amending Ill. Rev. Stat. 1991, ch. 38, par. 1003 — 6—3).) Pertinent here, the act rendered ineligible for the multiplier inmates *359convicted of criminal sexual assault, felony criminal sexual abuse, and aggravated criminal sexual abuse, and aggravated battery with a firearm, as well as related inchoate offenses. Pub. Act 88 — 311, eff. August 11, 1993 (amending Ill. Rev. Stat. 1991, ch. 38, par. 1003 — 6—3).
Pursuant to a certified class action, the circuit court of Cook County ruled that Public Act 88 — 311 violates ex post facto prohibitions. The suit had been brought by Michael Barger and Richard Maez, convicted, respectively, of criminal sexual assault and attempted armed robbery. Barger and Maez represented inmates whose crimes and convictions fell between September 10, 1990, the effective date of Public Act 86 — 1373, and August II, 1993, the effective date of Public Act 88 — 311, making them ineligible for increased credit. Finding Public Act 88 — 311 unconstitutional, the circuit court permanently enjoined the Department of Corrections from applying it to the plaintiff class.
The matter lies here on direct appeal (134 Ill. 2d R. 302).
DISCUSSION
The Federal Constitution prohibits States from enacting any ex post facto law. (U.S. Const., art. I, § 10.) Although that limitation renders it unnecessary, the same protection historically has been included in this State’s constitutions. (Ill. Const. 1970, art. I, § 16; Ill. Const. 1870, art. II, § 14; Ill. Const. 1848, art. XIII, § 17; III. Const. 1818, art. VIII, § 16; F. Grad, The State Bill of Rights, in Con-Con, Issues for the Illinois Constitutional Convention 44 (V. Ranney ed. 1970); G. Braden & R. Cohn, The Illinois Constitution: An Annotated and Comparative Analysis 75 (1969).) It has been suggested that there is, nevertheless, some utility in the provisions’ coexistence, the thought being that the prohibitions, together, lend greater assurance of the constitu*360tional protection than the Federal clause alone. G. Braden & R Cohn, The Illinois Constitution: An Annotated and Comparative Analysis 75 (1969).
But the drafters of our modern constitution intended the Illinois ex post facto clause to do no more than conform to the Federal Constitution’s general prohibition on the States. (3 Record of Proceedings, Sixth Illinois Constitutional Convention 1476; 6 Committee Proposals, Sixth Illinois Constitutional Convention 55.) Thus, in construing this State’s constitutional provision, we are without a basis to depart from the Supreme Court’s construction of the Federal ex post facto clause. (See People v. Tisler (1984), 103 Ill. 2d 226, 243-45.) And, in fact, this court has long interpreted our own constitutional provision in step with Supreme Court pronouncements. See, e.g., People v. Ramey (1992), 152 Ill. 2d 41, 63-64.
In Weaver v. Graham (1981), 450 U.S. 24, 67 L. Ed. 2d 17, 101 S. Ct. 960, the Supreme Court used an expansive interpretation of the ex post facto clause to strike down a Florida statute which reduced "gain-time” credit earned for avoiding disciplinary infractions and performing assigned tasks. Such legislation, the Court explained, could be constitutionally applied retrospectively only if it did not work to a prisoner’s "detriment.” (Weaver, 450 U.S. at 33, 67 L. Ed. 2d at 25, 101 S. Ct. at 966.) Because the statute "change[d] 'the quantum of punishment’ ” for prisoners who committed crimes before its enactment, it was disadvantageous with respect to them. (Weaver, 450 U.S. at 33, 67 L. Ed. 2d at 25, 101 S. Ct. at 966, quoting Dobbert v. Florida (1977), 432 U.S. 282, 293-94, 53 L. Ed. 2d 344, 356, 97 S. Ct. 2290, 2298.) The disadvantage: constricting the opportunity to earn early release effectively "lengthenfed]” the period of actual incarceration, making more onerous the punishment for already committed crimes. Weaver, *361450 U.S. at 33-34, 67 L. Ed. 2d at 26, 101 S. Ct. at 966-67.
This court, in Tiller v. Klincar (1990), 138 Ill. 2d 1, used the same interpretation of the ex post facto prohibition to invalidate legislation curtailing the frequency of parole hearings which had been previously mandated every year. The "possibility of parole,” the court noted, "is an element of the punishment annexed to any crime.” (Tiller, 138 Ill. 2d at 11.) Thus, in lengthening the period between parole hearings, the legislation eliminated the opportunity for earlier release to the disadvantage of those already incarcerated. Tiller, 138 Ill. 2d at 11-12.
The notion that the ex post facto prohibition nullifies any law which " 'alters the situation of a party to his disadvantage’ ” (emphasis omitted) was established in Kring v. Missouri (1883), 107 U.S. 221, 228-29, 27 L. Ed. 506, 509, 2 S. Ct. 443, 449, quoting United States v. Hall (D. Pa. 1809), 26 F. Cas. 84, 86 (No. 15,285). But, in Collins v. Youngblood (1990), 497 U.S. 37, 48-49, 111 L. Ed. 2d 30, 42-43, 110 S. Ct. 2715, 2722, the Supreme Court overruled Kring, holding that the quoted language indicated an unjustified expansion of the ex post facto prohibition beyond the categories of laws the Framers intended to come within the clause’s ambit.
Those categories were established in Calder v. Bull (1798), 3 U.S. (3 Dall.) 386, 1 L. Ed. 648, shortly after ratification of the Constitution. They included, as is relevant here, "[ejvery law that changes the punishment, and inflicts a greater punishment, than the law annexed to the crime, when committed.” (Emphasis in original.) (Calder, 3 U.S. (3 Dall.) at 390, 1 L. Ed. at 650.) Summarized differently, such a law would be one "which makes more burdensome the punishment for a crime[ ] after its commission.” (Beazell v. Ohio (1925), 269 U.S 167, 169-70, 70 L. Ed. 216, 217, 46 S. Ct. 68, 68.) If the law does *362not so affect the punishment associated with a crime, it is of no moment that the law may work to a prisoner’s disadvantage. See Collins, 497 U.S. at 48, 111 L. Ed. 2d at 42-43, 110 S. Ct. at 2722.
The question here then becomes whether elimination of an opportunity to increase good-conduct credit is a change in the punishment associated with a crime or results in the infliction of greater punishment. In the wake of Collins, that question is not to be answered against what disadvantage may be visited upon the plaintiff class through elimination of the opportunity for early release. But because Collins otherwise left unaffected the Court’s holding in Weaver and, by implication, this court’s decision in Tiller, the question ultimately turns on the meaning the Court ascribes to the term "punishment.”
The Supreme Court does not view punishment for ex post facto clause purposes to mean simply the period of incarceration prescribed by a judge for a person convicted of a crime — that is, the sentence. Instead, the Court construes punishment to mean the actual time that such a person spends in prison. The Florida statute invalidated in Weaver did not affect, retrospectively, the sentence imposed on any inmate. The " 'quantum of punishment’ ” affected was nothing but the time for which an inmate was actually incarcerated under the sentence imposed. Generally, then, any legislation curtailing the possibility of reducing actual prison time makes more onerous the consequence associated with a crime. It is entirely inconsequential that capitalizing on the opportunity may depend on an inmate’s success in staying out of trouble or attaining other goals.
Public Act 88 — 311 does not change the prescribed period of incarceration imposed for the crimes committed by members of the plaintiff class. If understanding the consequence associated with a crime was limited by *363the more common notion of equating punishment with sentence, the act would comport with the constitutional clauses. But when the consequence associated with a crime is viewed in the manner indicated by the Supreme Court in Weaver, the act does, indeed, make more burdensome the punishment associated with certain crimes already committed.
We must, as in Tiller, apply that more generous understanding of punishment here. Public Act 88 — 311 curtails the opportunity for an earlier release as permitted under section 3 — 6—3 in its form as existed between September 10, 1990, and August 11, 1993. Public Act 88 — 311 curtails the opportunity for an earlier release as permitted under section 3 — 6—3 in its form as existed between September 10, 1990, and August 11, 1993, and so makes more burdensome the punishment associated with the crimes of the plaintiff class. The class consists of inmates who were eligible as of September 10, 1990, to enhance their good-conduct credit by a factor of 1.25 under section 3 — 6—3 but who were, as of August 11, 1993, deprived of that opportunity by Public Act 88 — 311. As to that class, Public Act 88 — 311 violates the ex post facto prohibitions of the Federal and Illinois Constitutions.
We therefore affirm the permanent injunction entered by the circuit court. The injunction precludes application of Public Act 88 — 311 "to persons who committed the offenses for which they were convicted on and after September 10, 1990[,] to and including August 10, 1993, were committed to the Illinois Department of Corrections, and were or would have been eligible on August 10, 1993[,] for the 1.25 enhanced educational good conduct credit” under section 3 — 6—3 as unamended by Public Act 88 — 311.
Affirmed.