The defendant, Richard Chris Berte, was indicted for home invasion committed with a firearm (G. L. c. 265, § 18C), armed robbery (G. L. c. 265, § 17), and *30conspiracy to distribute a class B drug (G. L. c. 94C, § 40).1 After a jury-waived trial, a Superior Court judge found him guilty of armed home invasion and armed robbery, and acquitted him of the drug conspiracy charge. The judge sentenced the defendant to twenty years to twenty years and a day in State prison on the home invasion charge, and a concurrent sentence of eighteen to twenty years for the armed robbery.
The principal issue on appeal is whether G. L. c. 265, § 18C, the home invasion statute, is unconstitutional on its face because of various infirmities in its penalty section.2 See Commonwealth v. Brown, 431 Mass. 772, 779-781 (2000). Prior to 1998, which was the year of the statute’s amendment, G. L. c. 265, § 18C, inserted by St. 1993, c. 333, permitted a sentencing judge to impose, upon conviction of armed home invasion, an indeterminate sentence “in the state prison for fife or for any term of not less than twenty years.”
By St. 1998, c. 180, § 57, a twenty-year sentence in the State prison was added to the sentencing scheme for those offenders who commit the crime “while being armed with a firearm, shotgun, rifle, machine-gun, or assault weapon.” Mindful that the Supreme Judicial Court had identified serious problems with the amendment in the Brown case,3 the defendant contends, as he did prior to his sentencing in the Superior Court, that the *31penalty scheme under which he was tried and convicted is facially unlawful and unconstitutionally vague and ambiguous. First, the defendant argues that the statute’s twenty-year fixed term for the aggravated home invasion portion of the statute conflicts with G. L. c. 279, § 24.* **4 Second, he claims that it inconsistently also mandates a ten-year minimum sentence.5 Third, the defendant argues that the statute runs counter to G. L. c. 127, § 133, because it allegedly permits a partial suspended sentence for first-time offenders.6 Fourth, the defendant submits that the statute inconsistently provides for and prohibits probation. There is an ancillary argument that because the judge had agreed prior to trial that the minimum sentence on the home invasion charge was ten years (rather than the twenty-year minimum pursuant to which the defendant was sentenced), the defendant’s waiver of his right to a jury trial was not knowing or intelligent.
1. Vagueness challenge. “A facial challenge to the constitutional validity of a statute is the weakest form of challenge, and the one that is the least likely to succeed. A statute so questioned is presumed constitutional. A court may interpret a statute to set forth considerations to clarify and specify, and, where necessary, to narrow, the statute’s terms in order that it may be held constitutional.” Blixt v. Blixt, 437 Mass. 649, 652 (2002) (citations omitted).
*32(a) The apparently determinate sentence language employed here has been construed before. In Commonwealth v. Lightfoot, 391 Mass. 718, 721 (1984), the court, interpreting G. L. c. 272, § 7, explained that in the absence of the word “mandatory,” a statutory imperative that the judge “ ‘shall’ impose a five-year sentence” does not preclude judicial discretion in sentencing. Contrast Commonwealth v. Marrone, 387 Mass. 702, 704-707 (1982) (portion of statute requiring “mandatory term of fifteen years” held invalid as violation of G. L. c. 279, § 24). This is so particularly in light of the next sentence in the statute in the Lightfoot case, which states that the five-year sentence cannot be reduced to less than two years. See Commonwealth v. Lightfoot, supra. The court in Lightfoot explained, “This indicates the minimum sentence which a judge may impose. The following portion of the second paragraph reveals that a two-year sentence must be served because it cannot be suspended. Nor can the defendant receive probation, parole, furlough, or a deduction from his sentence for good conduct or otherwise. We believe that the Legislature chose this particular format to reflect its desire to ensure a two-year mandatory minimum sentence.” Ibid.
The sentencing structure at issue here mirrors that illustrated in Lightfoot, and we interpret it the same way, that is, as simply another format for stating the minimum and maximum sentencing range. Because the judge sentenced the defendant to a maximum term of twenty years and a day, she exceeded her authority under the statute.
The incongruity of this result is not lost on us, and we cannot fault the judge for her error. The dicta in Commonwealth v. Brown, supra at 780-781, seemingly contradicts the holding in Lightfoot by characterizing this statutory language as a single-term penalty of twenty years and a prohibition against reduction to less than ten years when the applicable good conduct and parole procedures already made such a reduction impossible.
Following Brown, the judge attempted to sentence the defendant to the twenty-year term she believed the statute required while saving the sentence from conflict with G. L. c. 279, § 24, by adding the maximum term of twenty, years and a day. This sentence is identical to that upheld in Brown, see id. *33at 781; however, the defendant in Brown was subject to that portion of the statute dealing with armed home invasion accomplished with a weapon other than a firearm, for which the statutory sentencing range is twenty years to life, see id. at 773, rather than the portion covering armed home invasion with a firearm.
As the court noted in Brown, the 1998 amendment imposes a significantly lesser sentence (ten to twenty years, rather than twenty years to life) on what is intuitively a more serious crime (armed home invasion with a firearm, rather than with some presumably less dangerous weapon). While we might believe this to be indicative of legislative oversight, see id. at 781, the language of the statute is clear, see id. at 780 n.12, and we “will not interpret a . . , criminal statute so as to increase the penalty that it places on an individual when such an interpretation can be based on no more than a guess as to what [the Legislature] intended.” Commonwealth v. Marrone, supra at 705, quoting from Ladner v. United States, 358 U.S. 169, 178 (1958). “We are not free to ignore or to tamper with that clear expression of legislative intent. If the law is to be changed, the change can only be made by the Legislature.” Commonwealth v. Villalobos, 437 Mass. 797, 804 (2002), quoting from Commonwealth v. Jones, 417 Mass. 661, 664 (1994).
(b) The defendant’s claims regarding § 18C’s inconsistent provision of suspended sentences and probation are unavailing. Although we agree that the statute appears to countenance partial suspended sentences for first time offenders,7 G. L. c. 127, § 133, states that “[sentences of imprisonment in the state prison shall not be suspended in whole or in part.” Because we read statutes relating to the same subject matter as “an harmonious whole,” Commonwealth v. Smith, 431 Mass. 417, 424 (2000), quoting from Board of Educ. v. Assessor of Worcester, 368 Mass. 511, 513-514 (1975), we conclude that § 18C cannot be so interpreted. The statute does not state that first time offenders may receive suspended sentences, and we will not read it to imply such a provision.
*34(c) The defendant’s assertions that the statute is inconsistent in its probation provisions also fail. The statute begins by prohibiting probation, goes on to prohibit probation for anyone over the age of seventeen, and concludes by prohibiting probation for repeat offenders.8 At first glance, nothing more seems to be happening than a prohibition of probation, but the defendant claims that the additional provisos seem to allow probation in certain circumstances. We encourage the Legislature to examine this part of the statute and amend it if our interpretation does not comport with its intention, but we determine that the only rule to be gleaned from the statute as written is that probation is prohibited. It may not apply to those over age seventeen, nor to those who have committed a second offense under the statute, nor to anyone who is convicted of violating this law. See Commonwealth v. Villalobos, supra.
2. Waiver of jury trial. We need not dwell at length on the question whether the record demonstrates affirmatively that the defendant’s jury waiver was “knowingly and intelligently” made. See generally Commonwealth v. Dietrich, 381 Mass. 458, 460-461 (1980), citing Schneckloth v. Bustamonte, 412 U.S. 218, 237-238 (1973). The judge in the instant case advised the defendant of the right to a jury trial and of the consequences that result when a bench trial takes place. The defendant executed and filed a written waiver pursuant to G. L. c. 263, § 6, and prior to signing the waiver, the judge engaged the defendant in a thorough colloquy concerning his decision. See Commonwealth v. Hardy, 427 Mass. 379, 382 (1988).
Without citation to any authority, the defendant claims that the colloquy nevertheless was deficient because the judge informed him that the minimum sentence under the armed home invasion charge was ten years, only to reconsider and determine, post-waiver, that the minimum was twenty years. The defendant’s argument fails, however, because the statutory minimum *35sentence would be the same regardless of his choice to proceed without a jury. Confusion and misinformation regarding the statutory minimum sentence does not impair the knowing and intelligent nature of the defendant’s waiver of his right to a jury trial, because the two are not related issues.
The defendant claims that the judge would have penalized him had he exercised his right to a jury trial, and that the judge in this case determined that an understanding of the minimum punishment on this charge was a precondition to the defendant’s voluntary waiver. There is no support in the record for either claim.
The convictions for home invasion committed with a firearm and for armed robbery, and the sentence on the conviction for armed robbery, are affirmed. The sentence on the conviction for home invasion committed with a firearm is vacated, and the case is remanded for resentencing on this count with a maximum sentence not to exceed twenty years, and a minimum sentence of ten years imprisonment.
So ordered.