— In this personal restraint petition, petitioner Larry Quackenbush challenges the authority of the Indeterminate Sentence Review Board (Board) to rescind its final discharge order under the 1993 amendment to the final discharge statute, RCW 9.96.050. The Board returned Quackenbush to the custody of the Department of Corrections when it discovered Quackenbush had violated his parole. We hold that a final discharge issued under RCW 9.96.050 does not divest the Board of authority to rescind the final discharge of an offender who violates the conditions of parole prior to final discharge. Accordingly, we *930affirm the Court of Appeals’ order dismissing Quackenbush’s petition.
FACTS
Quackenbush was convicted of second-degree murder in 1980 and sentenced to a maximum term of 30 years in prison. He was initially paroled in August 1985, but parole was revoked after he committed parole violations. Three years later, in April 1988, Quackenbush was again released on parole, this time to California where he had family. He was again charged with violating the conditions of his parole, but the Board reinstated Quackenbush’s parole on September 2, 1989.
Quackenbush continued to engage in criminal activities. In January 1993, he committed three robberies and possessed a firearm and heroin in violation of the conditions of his parole. Prosecutors in three separate California counties charged Quackenbush for these felonies. Between May 1993 and April 1994, Quackenbush was tried, convicted, and subsequently sentenced to maximum terms ranging from one year to five years in prison.
Unaware of these recent California convictions the Board issued a final discharge to Quackenbush in July 1993 and restored his civil rights. See RCW 9.96.050. Two months later, in September 1993, the Board learned of Quackenbush’s convictions and rescinded the final discharge order. The Board then issued a warrant suspending Quackenbush’s parole, deferring action so that Quackenbush could serve his sentences in California.
In September 1998, Quackenbush was extradited to Washington. Following a parole revocation hearing in which Quackenbush admitted the alleged violations, the Board revoked parole and placed Quackenbush in the custody of the Washington State Department of Corrections. Quackenbush’s maximum release date is now December 10, 2009.
Quackenbush filed a personal restraint petition in which *931he claimed that the Board lacked authority to rescind the final discharge which resulted in his return to prison. Chief Judge Bridgewater dismissed the petition, ruling that the Board had discretion to revoke parole any time before the expiration of Quackenbush’s maximum sentence.
ANALYSIS
We are asked to decide whether the Board has authority to return a parolee to prison once a final discharge from parole is issued under RCW 9.96.050, the final discharge statute. Although this court has not interpreted the Board’s authority following a 1993 amendment to the statute, the power of the Board under earlier versions of the statute has been the subject of a number of opinions.
The Board was created by statute in 1935.1 See Laws of 1935, ch. 114, § 1; Rem. Rev. Stat. § 10249-1 (Supp. 1947). Ten years later, in In re Application of Costello, 22 Wn.2d 697,157 P.2d 713 (1945), this Court considered whether the Board had authority under the 1935 statute to discharge an offender from all obligations imposed by the Governor’s conditional pardon. Costello, 22 Wn.2d at 704. Recognizing that the statute dealt only with the Board’s authority to parole, the Court held that the Board did not have the power to issue a final discharge to an offender, which would relieve the defendant from serving any conditions added by the governor to the offender’s sentence or to nullify the governor’s right to revoke the defendant’s pardon for a violation of such conditions. Costello, 22 Wn.2d at 705.
The Court revisited the 1935 statute in Scott v. Callahan, 39 Wn.2d 801, 239 P.2d 333 (1951). The petitioner Scott had been sentenced to a term of not more than 15 years in prison. Scott, 39 Wn.2d at 802. After he served five years of his sentence, the Board released him on parole. Scott, 39 Wn.2d at 802. A year later, the Board issued a final discharge from supervision, releasing him from all obliga*932tions imposed by parole. Scott, 39 Wn.2d at 802. Four years later, the Board revoked Scott’s parole because he engaged in conduct specifically prohibited by conditions of his parole. Scott, 39 Wn.2d at 803. Scott brought a habeas corpus petition, alleging the Board lost jurisdiction over him when it entered the final discharge.
This Court affirmed the Board’s continuing jurisdiction and its rescission of final discharge, holding that:
[t]he Board has no power, statutory or otherwise, to affect his maximum sentence in any matter. Its power is limited to permitting a convicted person to leave the enclosure of the penitentiary after he has served a period of confinement fixed for him by the Board in accordance with [the statute].
Scott, 39 Wn.2d at 804. The Court observed that while the Board may discharge a parolee from parole conditions, the Board “cannot enlarge or extend the term fixed by the court’s commitment, nor can it discharge a convict from custodia legis before the expiration of the maximum term for which he has been sentenced.” Scott, 39 Wn.2d at 805 (citation and emphasis omitted) (citing In re Writ of Mandamus of Wyback, 32 Wn.2d 780, 203 P.2d 1083 (1949)). In other words, a final discharge was not the end of the sentence but rather the end of active supervision by the Board.
Against this backdrop, the Legislature enacted the final discharge statute, RCW 9.96.050. Laws op 1961, ch. 187, § 1. The former version of the statute stated in relevant part:
When a prisoner on parole has performed the obligations of his release for such time as shall satisfy the Board of prison terms and paroles that his final release is not incompatible with the best interests of society and the welfare of the paroled individual, the Board may make a final order of discharge . . . to the prisoner: Provided, That no such order of discharge shall be made in any case within a period of less than one year from the date on which the board has conditionally discharged the parolee from active supervision by a probation and parole officer, except where the parolee’s sentence expires earlier thereto.
*933Former RCW 9.96.050 (1961) (emphasis added.) Under the original version of the statute the Board had discretion to issue a final discharge from active parole, provided the discharge was entered at least one year following an order of conditional discharge from active supervision. See former RCW 9.96.050. Furthermore, the Board had continuing jurisdiction over a person released on conditional parole. See Honore v. State Bd. of Prison Terms & Paroles, 77 Wn.2d 697, 700, 466 P.2d 505 (1970) (holding that the Board does not lose jurisdiction by paroling a felon to the federal courts on a federal indictment, and that jurisdiction is retained until the expiration of the maximum sentence).
In 1993, the Legislature amended RCW 9.96.050, deleting the requirement of a one-year wait between the conditional and final discharge and providing that:
If not earlier granted, the board shall make a final order of discharge three years from the date of parole unless the parolee is on suspended or revoked status at the expiration of the three years.
Laws of 1993, ch. 140, § 4.2
Quackenbush does not claim that the Board lacked authority to issue a final discharge from parole. Instead, the parties disagree on the import of a final discharge from parole. Quackenbush argues that a final discharge divests the Board of jurisdiction, and that the Board therefore did not have the power to rescind the final discharge and return him to prison. He contends that Scott is no longer controlling because the 1993 amendment extinguishes the Board’s discretionary power by making the final discharge of all parolees automatic after three years, except for those who have had parole suspended or revoked. In other words, Quackenbush reasons, the Board was not exercising discretion when it issued the final discharge from parole; instead, the Board was executing its statutorily mandated duty to discharge him. Thus, he argues, a final discharge divests *934the Board of power to revoke parole, even if an offender admits to committing acts prior to the final discharge which constitute violations of conditions of his parole.
The State responds that Quackenbush has confused a final discharge from parole with a reduction in sentence, and that the Board does not have the power to reduce sentences. The State relies only on cases that predate the 1993 amendment to RCW 9.96.050 for that proposition. We note, however, that this Court has consistently held that the Board lacks the power to reduce, increase, or otherwise alter the maximum sentence imposed by the trial court. In re Personal Restraint of Ayers, 105 Wn.2d 161, 167, 713 P.2d 88 (1986); Honore, 77 Wn.2d 697; In re Writ of Habeas Corpus of Mason, 42 Wn.2d 610, 615, 257 P.2d 211, cert. denied, 346 U.S. 901 (1953); Scott, 39 Wn.2d 801.
Statutory construction is a question of law which we review de novo. State v. Martin, 137 Wn.2d 774, 788, 975 P.2d 1020 (1999). Our principal duty is to “ascertain and give effect to the intent of the Legislature.” Nat’l Elec. Contractors Ass’n v. Riveland, 138 Wn.2d 9, 19, 978 P.2d 481 (1999). The language of the amendment does not suggest that the Legislature intended a final discharge from parole to have the effect of terminating the court’s sentence. The statute describes the effect of a final discharge: “[s]uch discharge, regardless of when issued, shall have the effect of restoring all civil rights” but “shall not restore the right to receive, process, own, or transport firearms.” RCW 9.96.050. In the only reference to the maximum sentence or the Board’s jurisdiction, the statute provides that “[t]he board retains the jurisdiction to issue a certificate of discharge after the expiration of the prisoner’s or parolee’s maximum statutory sentence.” RCW 9.96.050 (emphasis added). Rather than limiting the Board’s jurisdiction, RCW 9.96.050 actually extends the Board’s authority beyond its historic boundary, the expiration of the maximum sentence.
If the Legislature had intended to change something as *935basic as the nature of a final discharge, it would have simply stated such a change as its objective. Merely removing discretion as to how long the Board can keep a conforming parolee under supervision does not indicate any Legislative intent to change the statute’s meaning otherwise or to depart from the long-standing interpretation of the statute: final discharge is simply suspension of active supervision until the end of the maximum sentence. Honore, 77 Wn.2d at 700 (holding that parolee may be returned to the Board’s custody for completion of the sentence); Scott, 39 Wn.2d at 804 (holding that the Board could not relinquish power over the parolee until expiration of the maximum sentence); Costello, 22 Wn.2d at 707 (holding that the Board did not have the power to issue a final discharge to an offender whose maximum sentence had not been served).
We will not step into the role of the Legislature and judicially alter the nature of a final discharge. See Davis v. Dep’t of Licensing, 137 Wn.2d 957, 976 n.12, 977 P.2d 554 (1999) (the courts should not second-guess the wisdom of the Legislature in making policy decisions unless those decisions violate constitutional principles); Millay v. Cam, 135 Wn.2d 193, 203, 955 P.2d 791 (1998) (courts do not amend statutes by judicial construction).
The legislative history underlying the 1993 amendment, while scant, lends support to our conclusion. According to the Bill Report, the Board requested revisions to the parole scheme in order to make it more consistent with the Sentencing Reform Act of 1981 (SRA).3 See Senate Comm, on Law and Justice, S.B. Rep. SB 5060 (Wash. Feb. 4,1993). The SRA establishes a strict schedule of sentences for crimes depending on a variety of objective factors, rather than *936allowing the Board to set mínimums as it sees fit. According to a similar committee report in the House, the Board was concerned about the disparity in the different sentencing schemes; the SRA allows only for supervision of certain offenders after release from prison, whereas the indeterminate system requires much greater monitoring. See House Comm, on Corrections, H.B. Rep. SB 5060 (Wash. 1993). This report says in relevant part:
If a parolee is found in one of the following circumstances a final order of discharge shall be entered by the board. Offenders on parole longer than three years who are not on suspended or revoked status will be discharged. Offenders on parole for up to three years, who are not on suspended or revoked status will be discharged as determined by the board. Parolees are not required to be on conditional discharge for one year prior to a final discharge order.
House Comm, on Corrections, H.B. Rep. SB 5060, at 2. While this history does not shed a great deal of light, it appears that the Legislature intended to reduce the number of offenders on parole to achieve some consistency with SRA sentencing provisions relating to supervision after release from prison. Also, while the 1993 amendment may have removed some of the Board’s discretion in granting a final discharge, it is reasonable to conclude that the statutory change was also designed, in part, for administrative convenience; that is, offenders on parole for three years would not be required to remain on active supervision for life. We note that the Board is scheduled to go out of existence on June 30, 2008. RCW 9.95.0011(1). The limited legislative history tends to suggest that a final discharge from parole suspends the Board’s active supervision, rather than terminating the sentence early.
Additionally, the Legislature was presumably familiar with this court’s treatment of final discharge when amending the statute. See Woodson v. State, 95 Wn.2d 257, 261-62, 623 P.2d 683 (1980) (“the legislature is presumed to know the existing state of the case law in those areas in which it is legislating”). Our cases have consistently held that a final *937discharge does not mean the end of the sentence, but merely the end of active supervision by the Board. See Scott, 39 Wn.2d at 805. Nowhere does the statute as amended say that a final discharge reduces the maximum sentence.
Quackenbush’s interpretation of the final discharge statute would preclude the Board from correcting its own errors. Agencies have a limited right to reopen their final decisions. St. Joseph Hosp. & Health Care Ctr. v. Dep’t of Health, 125 Wn.2d 733, 743, 887 P.2d 891 (1995); Hall v. City of Seattle, 24 Wn. App. 357, 362, 602 P.2d 366 (1979). In Hall, the Court of Appeals relied upon a decision by the Minnesota Supreme Court:
“Where through fraud, mistake, or misconception of facts the commissioner enters an order which he promptly recognizes may be in error, there is no good reason why, on discovering the error, he should not, after due and prompt notice to the interested parties, correct it.”
Hall, 24 Wn. App. at 362 (quoting Anchor Cas. Co. v. Bongards Co-Op. Creamery Ass’n, 253 Minn. 101, 106, 91 N.W.2d 122, 126 (1958)). An administrative agency has the authority to correct an obvious mistake when correction can be done promptly and fairly, even when the agency has made a final decision.4
In this case, Quackenbush was not eligible for final discharge because of the pending charges against him in California. Once the Board discovered these charges, it realized its error and promptly rescinded the discharge. *938The language of the final discharge document emphasizes the Board’s error:
WHEREAS, It has further been made to appear that the said person, since so paroled, has performed in a satisfactory and acceptable manner and has given such evidence as to justify the belief that said person is trustworthy and reliable and will remain at liberty without violating the laws of this state or nation, and that the final release and discharge is compatible with the welfare of society ....
Quackenbush had not proved himself trustworthy and his release was not compatible with the welfare of society, as evidenced by his felonious behavior while on parole in California. Under such circumstances, the Board had authority to correct its obvious error.
CONCLUSION
Under RCW 9.96.050, the term "final discharge from parole” means discharge from active supervision by the Board. The Board had the power to rescind the final discharge that it had issued in error. The Court of Appeals is affirmed.
Ireland and Bridge, JJ., and Guy and Talmadge, JJ. Pro Tern., concur.
The Indeterminate Sentence Review Board was formerly known as the Board of Prison Terms and Paroles. RCW 9.95.009(1).
The Legislature has amended RCW 9.96.050 numerous times since it was originally enacted. The current version of RCW 9.96.050 took effect the day before the Board issued the final discharge from parole to Quackenbush.
The Sentencing Reform Act of 1981 (SRA), chapter 9.94A RCW changed the Washington sentencing scheme from primarily indeterminate sentences to determinate sentences. Generally, the SRA limits supervision after release from prison. For example, certain offenses are subject to one year supervision, whereas more serious offenses may be supervised for a maximum term of two years or the amount of earned early release time, whichever is longer. Under indeterminate sentencing, however, parole supervision may continue up to the maximum term for the crime.
At least as to prisoners for whom the three-year period had not already passed when the 1993 Amendment took effect, the Board can avoid the type of problem that occurred here by complying with ROW 9.95.140. That section directs the Board to “cause a complete record to be kept of every prisoner under the jurisdiction of the board released on parole” and to organize those records “in accordance with the most modem methods of filing and indexing so that there always will be immediately available complete information about each such prisoner.” Better record keeping would not have helped here, however, because Quackenbush had already been on parole for more than three years when he was convicted of the new offenses in January 1993, and when the new statute took effect later that year. The Board’s awareness of the California convictions when it granted his final discharge in June 1993 would not have altered that fact.