PRESIDING JUSTICE HOPKINS delivered the opinion of the court:

On December 18, 2000, Robert Taylor (the petitioner) filed in the circuit court a prose petition for a writ of habeas corpus seeking his release from the Illinois Department ofCorrections. In his petition, the petitioner alleged that his sentence of natural-lifeimprisonment was unconstitutional under Apprendi v. New Jersey, 530 U.S. 466, 147 L. Ed.2d 435, 120 S. Ct. 2348 (2000), that he had served his prison term under the sentencingstatute in place at the time of his conviction, and that he was entitled to his immediate releasefrom incarceration. The trial court dismissed the petitioner's petition for a writ of habeascorpus, and the petitioner's appeal followed. On appeal, the petitioner asserts that the trialcourt erred in dismissing his petition for a writ of habeas corpus. We affirm.

Following a bench trial, the petitioner was convicted of murder (Ill. Rev. Stat. 1979,ch. 38, par. 9-1(d)) and of armed robbery (Ill. Rev. Stat. 1979, ch. 38, par. 18-2). The trialcourt sentenced the petitioner to death for the murder conviction and to a 60-year, extended-term sentence for the armed robbery conviction. On appeal, the supreme court held that theevidence was insufficient to sustain the petitioner's armed robbery conviction and reversedhis conviction. People v. Taylor, 101 Ill. 2d 508 (1984). The supreme court also vacatedthe petitioner's death sentence and remanded his case to the circuit court for a newsentencing hearing for his murder conviction, with directions to impose a sentence otherthan death. Taylor, 101 Ill. 2d at 525.

On remand, the trial court determined that, even though the petitioner was notcharged with the offense, the evidence at the trial was sufficient to sustain a conviction forburglary (Ill. Rev. Stat. 1979, ch. 38, par. 19-1(a)). Because factors in aggravation werepresent, i.e., the murder had been committed during the course of a burglary and had beenbrutal and heinous indicative of wanton cruelty, the court imposed a sentence of natural-lifeimprisonment pursuant to section 5-8-1(a)(1) of the Unified Code of Corrections (UnifiedCode) (Ill. Rev. Stat. 1979, ch. 38, par. 1005-8-1(a)(1) (now see 730 ILCS 5/5-8-1(a)(1)(b)(West 2000))). The petitioner appealed, contending that the trial court's findings that theburglary and the commission of an exceptionally brutal and heinous murder wereaggravating factors warranting a life sentence were error. The appellate court affirmed thetrial court's holding that the evidence in the record supported a finding of the petitioner'sguilt beyond a reasonable doubt for the commission of the offense of burglary, and itaffirmed the trial court's imposition of a life sentence. People v. Taylor, 164 Ill. App. 3d 938(1987). The appellate court also affirmed the trial court's holding that the petitioner'sconduct in the commission of the murder had been exceptionally brutal and heinousindicative of wanton cruelty. Taylor, 164 Ill. App. 3d at 943. The Illinois Supreme Courtdenied the petitioner's leave to appeal. People v. Taylor, 119 Ill. 2d 572 (1988).

The petitioner filed his writ of habeas corpus after the United States Supreme Court'sdecision in Apprendi, which held that a sentence is unconstitutional if a fact used to increasethe maximum penalty for a crime is not submitted to a jury and proven beyond a reasonabledoubt. Apprendi, 530 U.S. at 490, 147 L. Ed. 2d at 455, 120 S. Ct. at 2362-63. In hispetition, the petitioner asserted that because the trial court based its sentence of natural-lifeimprisonment on the statutory aggravating factor that the murder committed had beenaccompanied by brutal and heinous conduct indicative of wanton cruelty, a sentencingenhancement not pled in the indictment, submitted to the jury, or proved beyond areasonable doubt, his sentence was unconstitutional under Apprendi and the extended-termsentencing statute under which he had been sentenced was void. Further, the petitionerclaimed that under the sentencing statute in place at the time of his conviction, he could onlybe sentenced to 20 to 40 years' imprisonment (Ill. Rev. Stat. 1979, ch. 38, par. 1005-8-1(a)(1)) for the murder. The petitioner asserted that when day-for-day good time is applied,he has served more than 20 years of the maximum sentence that he could have been givenand is entitled to his immediate release. The State filed a motion to dismiss pursuant tosection 2-615 of the Code of Civil Procedure (735 ILCS 5/2-615 (West 2000)), claiming thatthe petitioner failed to allege sufficient facts to state a cause of action for habeas corpusrelief. The trial court granted the State's motion to dismiss. The petitioner appeals.

The petitioner argues that under the Habeas Corpus Act (the Act) (735 ILCS 5/10-101 et seq. (West 2000)), a prisoner is entitled to an immediate release from incarcerationif the term during which the prisoner may be legally detained has expired. 735 ILCS 5/10-123(2) (West 2000). Additionally, the petitioner asserts that the Act provides that a prisonermay be discharged where, although the original imprisonment was lawful, some subsequentact, omission, or event has occurred entitling the prisoner to a discharge. 735 ILCS 5/10-124(2) (West 2000). The petitioner claims that because his extended-term sentence was voidab initio under the holding in Apprendi, he has served more than the maximum term ofimprisonment for which he was lawfully detained and is entitled to a discharge under section10-123(2) of the Act (735 ILCS 5/10-123(2) (West 2000)). The petitioner further claimsthat the decision in Apprendi is a subsequent event entitling him to a discharge under section10-124(2) of the Act (735 ILCS 5/10-124(2) (West 2000)).

In a motion to dismiss under section 2-615, a trial court must consider whether theallegations of the complaint, when viewed in the light most favorable to the petitioner, aresufficient to state a cause of action upon which relief can be granted. LaPointe v. Chrans,329 Ill. App. 3d 1080 (2002). A trial court's grant of a motion to dismiss is reviewed denovo. LaPointe, 329 Ill. App. 3d at 1083. "A writ of habeas corpus is available only toobtain the release of a prisoner who has been incarcerated under a judgment of a court thatlacked jurisdiction of the subject matter or the person of the plaintiff or where there has beensome occurrence subsequent to the prisoner's conviction that entitles him to his release. [Citations.]" Freeman v. Cowan, 331 Ill. App. 3d 218, 219 (2002). Habeas corpus reliefis limited solely to the grounds specified in the Act and may not be used to reviewproceedings that do not exhibit one of the defects set forth therein, even though the allegederror involves a denial of constitutional rights. Schlemm v. Cowan, 323 Ill. App. 3d 318(2001).

The petitioner has not alleged that he is entitled to a release because the trial courtlacked jurisdiction, but he contends that his sentence is unconstitutional and void ab initiobecause of the holding in Apprendi. The petitioner asserts that after day-for-day good timeis considered, he has served his maximum sentence under the sentencing statute in effect atthe time of his conviction and is entitled to a discharge under section 10-123(2) of the Act. Section 10-123(2) provides that a prisoner, originally lawfully detained, is entitled to adischarge when the time for which he is legally detained has expired. 735 ILCS 5/10-123(2)(West 2000). Habeas corpus relief is not available to a person who is in custody by virtueof a final judgment of a circuit court, unless the time during which the petitioner may belegally detained has expired. Faheem-El v. Klincar, 123 Ill. 2d 291 (1988). A petitionermust be entitled to a discharge either because he has completed his legally imposed sentenceor because some factor listed in section 10-124 has occurred to entitle the petitioner to anearlier discharge. See Faheem-El, 123 Ill. 2d at 294-95.

Here, the petitioner is not entitled to a discharge under the Act. The petitioner iscurrently serving time for a life sentence, so his time of legal detainment has not expired. His argument that his prison term has expired rests on the crucial issue of whether hissentence is unconstitutional under Apprendi.

Even if, as the petitioner argues, the life sentence imposed on him is unconstitutionalunder Apprendi, the petitioner still does not meet the requirement that he is entitled to adischarge because his prison term has expired. The petitioner's sentence would be 20 to 40years' imprisonment under the statute in effect at the time of his sentencing. Regardless ofwhether the petitioner has earned day-for-day good-time credit under section 3-6-3(a)(2) ofthe Unified Code (Ill. Rev. Stat. 1979, ch. 38, par. 1003-6-3(a)(2) (now see 730 ILCS 5/3-6-3(a)(2) (West 2000))), he is not entitled to a discharge and is subject to the custody of theDepartment of Corrections until the maximum term of imprisonment that could legally,under the petitioner's reasoning, be imposed, here 40 years, and the three-year mandatorysupervised release imposed under section 5-8-1(d) of the Unified Code (Ill. Rev. Stat. 1979,ch. 38, par. 1005-8-1(d) (now see 730 ILCS 5/5-8-1(d) (West 2000))) have expired. Faheem-El, 123 Ill. 2d at 302. A prisoner is not entitled to a discharge from prison until hismandatory supervised release is served, because mandatory supervised release is a part ofa sentence. Blythe v. Lane, 194 Ill. App. 3d 451 (1990). A prisoner cannot be dischargeduntil either his mandatory supervised release is served at the conclusion of the imposedsentence or, if mandatory supervised release is granted before the maximum term hasexpired, until a discretionary discharge is granted under section 3-3-8(b) of the Unified Code(Ill. Rev. Stat. 1979, ch. 38, par. 1003-3-8(b) (now see 730 ILCS 5/3-3-8(b) (West 2000))). Blythe, 194 Ill. App. 3d at 454-55. Mandatory supervised release is a gift, not a statutoryright that can be invoked at the will of a prisoner, and a prisoner cannot demand a dischargebefore the expiration of the maximum term of his sentence. Blythe, 194 Ill. App. 3d at 457. Therefore, because the petitioner in the case sub judice has not served the maximum termof a sentence that could be imposed at the time he was sentenced, here 40 years'imprisonment, and he has not served his mandatory supervised release, he is not entitled toa discharge. Accordingly, the trial court properly dismissed his petition because thepetitioner could not allege any facts that would allow for habeas corpus relief.

Further, even if Apprendi were applicable to the petitioner's case, he would notprevail; therefore, we do not determine whether Apprendi is a subsequent event entitling himto an early discharge from his lawfully imposed sentence under section 10-124(2) of the Act(735 ILCS 5/10-124(2) (West 2000)). First, the petitioner's sentencing statute is not voidab initio as the petitioner asserts. In Hill v. Cowan, 202 Ill. 2d 151 (2002), the supremecourt reiterated that the void ab initio doctrine only applies to statutes unconstitutional ontheir face. Hill, 202 Ill. 2d at 156. It is difficult to successfully mount a facial challenge toa statute, for a statute is facially unconstitutional only if no set of circumstances exists underwhich the statute would be valid. Hill, 202 Ill. 2d at 157. If any situation exists to whichthe statute could be validly applied, a facial challenge fails. Hill, 202 Ill. 2d at 157.

Here, the petitioner's sentence was imposed under section 5-8-1(a)(1) (Ill. Rev. Stat.1979, ch. 38, par. 1005-8-1(a)(1) of the Unified Code (now see 730 ILCS 5/5-8-1(a)(1)(b)(West 2000))), which allowed the imposition of a sentence of natural-life imprisonment fora murder conviction if any of the aggravating factors listed in section 9-1(b) of the CriminalCode of 1961 (Ill. Rev. Stat. 1979, ch. 38, par. 9-1(b) (now see 720 ILCS 5/9-1(b) (West2000))) existed or if the murder was accompanied by exceptionally brutal or heinousbehavior indicative of wanton cruelty. Section 9-1(b)(6)(c) of the Criminal Code of 1961provided that an aggravating factor was present if the murder was committed during thecourse of one of the enumerated felonies, including burglary. Ill. Rev. Stat. 1979, ch. 38,par. 9-1(b)(6)(c). There are many circumstances that come to mind where this statute canbe validly applied. Any murder committed during the enumerated felonies, if the felony isproved beyond a reasonable doubt at the trial, would be a valid application of section 5-8-1(a)(1)(b) of the Unified Code. Therefore, the statute under which the petitioner wassentenced is not facially unconstitutional and is not void ab initio.

Second, the petitioner claims that his sentence was unconstitutional under Apprendibecause the aggravating factor that the murder was exceptionally brutal and heinousindicative of wanton cruelty was not charged in the indictment, submitted to the trier of fact,or proven beyond a reasonable doubt. Regardless of this claim, the fact remains that thepetitioner's life sentence was also imposed because it occurred during the commission of aburglary, an aggravating factor, standing alone, that allows the imposition of a life sentence. Ill. Rev. Stat. 1979, ch. 38, pars. 1005-8-1(a)(1), 9-1(b)(6)(c). In the petitioner's appeal ofhis resentencing, the petitioner's life sentence was affirmed, based upon a finding that themurder had been committed in the course of a burglary. Taylor, 164 Ill. App. 3d at 943. The appellate court found that the fact that the petitioner had committed the offense ofburglary during the murder was supported by the evidence of record beyond a reasonabledoubt. Taylor, 164 Ill. App. 3d at 943. Because evidence of the aggravating factor that thepetitioner had committed the murder in the course of committing a burglary was presentedto the trier of fact (the trial judge) and proven at the petitioner's trial beyond a reasonabledoubt, the petitioner's sentence of natural life does not violate Apprendi.

Further, although the petitioner contends that he was not charged with burglary, theerror is harmless, because the appellate court found that the evidence of record supportedthe finding that the petitioner committed the offense of burglary beyond a reasonable doubt. Taylor, 164 Ill. App. 3d at 943. The Supreme Court held in United States v. Cotton, 535U.S. 625, 152 L. Ed. 2d 860, 122 S. Ct. 1781 (2002), that the failure to include an elementof an offense in an indictment that would enhance the sentence imposed is harmless errorwhere the evidence of the element is overwhelming and essentially uncontroverted. TheSupreme Court further held that the sentence imposed in Cotton need not be vacated whenthe requirements of Apprendi were not met if the error did not seriously affect the fairness,integrity, or public reputation of the judicial proceedings. Cotton, 535 U.S. 625, 152 L. Ed.2d 860, 122 S. Ct. at 1786.

The petitioner cannot present any evidence that he is entitled to a discharge becausehe has served his sentence (735 ILCS 5/10-123(2) (West 2000)) or because of theoccurrence of a subsequent event that would entitle him to a discharge under the statute (735ILCS 5/10-124(2) (West 2000)). Because the petitioner can present no evidence entitlinghim to relief under the Act, we find that the trial court did not err in granting the State'smotion to dismiss the petitioner's petition for a writ of habeas corpus.

For the foregoing reasons, the judgment of the circuit court of Randolph County isaffirmed.

Affirmed.

MAAG and KUEHN, JJ., concur.