with whom Circuit Judges REINHARDT, BERZON, and RAWLINSON join, dissenting:
Congress has mandated that the government must comply with 21 U.S.C. § 851(a) before a court may increase the sentence on the basis of a prior conviction. Because the government did not do so in this case, the district court erred in imposing the mandatory minimum sentence. Therefore, I respectfully dissent.
I
The requirements of 21 U.S.C. § 851(a) are unambiguous and specific: Before a sentence is enhanced, the government must file an information “stating in writing the previous conviction or convictions upon which it intends to rely.”1 Id. The consequences for neglecting to adhere to the statutory requirements are also clear: “If the requirement is not satisfied, a court may not enhance a sentence even if the defendant has prior felony drug convictions.” United States v. Hamilton, 208 F.3d 1165, 1168 (9th Cir.2000), cert. denied, 531 U.S. 867, 121 S.Ct. 164, 148 L.Ed.2d 111 (2000). In Hamilton, we restated the rule in our circuit that § 851(a) *949“requires strict compliance with the procedural aspects.” Id. at 1169.
The primary difficulty with determining that the government complied with the procedural requirements of § 851(a) is that everyone acknowledges that it didn’t. The record is quite clear that the United States failed to serve the amended information prior to Severino’s change of plea hearing. Indeed, the district court specifically found this fact in its order denying Severino’s § 2255 motion, stating plainly that: “Cooper [the government attorney] was not able to have Dayan [Severino’s lawyer] or Severino served with copies of the information prior to the commencement of the Rule 11 plea hearing.” (emphasis added).
Further, the Assistant United States Attorney admitted at the change of plea hearing that he was “having some difficulty” with the requirements of § 851. He stated that he had filed an information that day, but remarked “I am not very confident that I have all the information that should be in that type of information,” and that “the shortness of getting these proceedings on has prevented me from getting this into the hands of the Court and counsel before this proceeding.” Thus, it is undisputed that neither Severino nor his counsel received a copy of the information prior to the change of plea hearing.
The government now relies on the service by mail rule. See Fed.R.Crim.P. 49(b) (incorporating Fed.R.Civ.P. 5(b)). It did not present that argument to the district court, and the record is devoid of any evidence that the information was, in fact, mailed before the hearing. The best the government can offer is the form certificate of service attached to its filing; however, that only indicates that the information was mailed the date of the hearing. This is insufficient to warrant setting aside on appeal the district court’s factual finding that neither Severino nor his lawyer were served with the information prior to the change of plea hearing, as required by § 851(a). Absent a district court finding that service occurred prior to the hearing, the court was without statutory authority to impose the enhanced sentence. Hamilton, 208 F.3d at 1169 (noting the service requirements of the statute).
That should end the matter. However, even if the government could produce positive proof that it filed the § 851 information and mailed a copy to Severino before his 10 a.m. plea hearing, such service would not comport with due process requirements. “The purpose of notice under the Due Process Clause is to apprise the affected individual of, and permit adequate preparation for, an impending ‘hearing.’ ” Memphis Light, Gas and Water Div. v. Craft, 436 U.S. 1, 14, 98 S.Ct. 1554, 56 L.Ed.2d 30 (1978). To comport with due process, “[t]he notice must be of such nature as reasonably to convey the required information.” Mullane v. Cent. Hanover Bank & Trust Co., 339 U.S. 306, 314, 70 S.Ct. 652, 94 L.Ed. 865 (1950).
Section 851 was enacted, in part, to fulfill this due process requirement. The statute “ensures proper notice so a defendant is able to challenge the information” and “allows a defendant to make an informed decision about whether or not to plead guilty.” Hamilton, 208 F.3d at 1168. It also permits a defendant “to plan his trial strategy with full knowledge of the consequences of a potential guilty verdict.” United States v. Johnson, 944 F.2d 396, 407 (8th Cir.1991).
If a criminal defendant is to be subjected to additional years — perhaps decades— in prison because of prior convictions, he must be afforded a meaningful opportunity to contest them. A defendant is entitled to notice, as well as a hearing. Slipping an envelope into a mailbox seconds before a hearing is not constitutionally adequate notice.
*950II
In the context of this case, the obvious question is why this matters. After all, Severino’s counsel at the time seemed to be doing everything he could to ensure that Severino would receive the sentence enhancement, and Severino didn’t seem to be voicing any personal objection. The answer is twofold. First, the information filed by the government was incorrect and could not have served as a basis for sentence enhancement and, upon a careful examination of the record, it is not apparent at all that Severino was making an informed choice to forfeit his right to challenge the information. Second, because of the peculiar limitations of § 851(a), the district court did not have authority to impose the sentence enhancement absent compliance with the procedural predicates. Thus, it was plain error for the court to impose a sentence in excess of statutory authority.
A
The government’s information was not only untimely served, but it was inaccurate. The information filed on the hearing date stated the predicate conviction as: “Possession of 1 ounce to 1 kilogram of cocaine, Massachusetts, 1992-1993.” However, Severino had not been convicted of that crime. His only alleged criminal activity in Massachusetts was Operating a Motor Vehicle Without a License and Operating an Uninsured Motor Vehicle — and he had not been convicted of those traffic offenses. Thus, Severino had a very legitimate basis on which to challenge the proposed sentence enhancement. However, Severino could not know that, of course, because he had not been served with the information prior to the hearing.
His attorney did not appear to be any more enlightened, indicating only that he knew of a conviction “back East.” Severino was not asked by the district court whether he understood he had a right to challenge the information. When his attorney was questioned by the district court as to whether he had discussed the right with Severino, he'responded only that he had informed Severino that the government needed a conviction.
There is no doubt that Severino and his attorney were having difficulty communicating. Indeed, we previously vacated Severino’s sentence and remanded for re-sentencing because neither the district court nor Severino’s counsel had informed Severino of his right to appeal his sentence. United States v. Severino, No. 99-35161, 1999 WL 1278048 (9th Cir. Dec. 30, 1999). Severino’s counsel acknowledged at the plea hearing that he had encountered difficulty in explaining the Sentencing Guidelines, not only because Severino could not speak English, but because “he had never seen a graph before.” However, his counsel represented to the court that Severino “seemed to understand” how the Guidelines worked after the interpreter explained it to him. There is no indication in the record that the interpreter had explained to Severino that a statutory mandatory minimum sentence would be imposed in lieu of the Guideline calculation.
The record reflects confusion at both the change of plea and sentencing hearing on the part of almost everyone.2 Both hear*951ings proceeded with long colloquies about the Sentencing Guidelines, rather than the imposition of a mandatory minimum sentence.
At the change-of-plea hearing, for example, the district court noted that the plea agreement “does not set out the parties’ prediction or understanding of how the guidelines would work beyond an agreement to the quantity of drugs.” The government prosecutor agreed that statement was “essentially correct.” When asked by the court what the government’s estimate of Severino’s criminal history category would be, government counsel responded: “I have some indication there is a criminal history, but I really do not feel adequately advised to say what his criminal history is.” Thereupon, the court explained in detail how Severino’s criminal history would affect the Sentencing Guideline calculation, how acceptance of responsibility might affect the calculation, and how his level of participation might affect a sentence under the Guidelines.
Indeed, the change-of-plea hearing might well have concluded without any mention of a potential mandatory minimum sentence had defense counsel not interrupted the proceedings to point out that there was a conviction “back East” that might bring in a mandatory minimum. Later, when the prosecutor informed the district court it was having “some difficulty” with § 851, he identified the erroneous Massachusetts conviction as the sole basis for the sentence enhancement. When asked by the district court whether the information referenced the same conviction that defense counsel had mentioned earlier, the prosecutor replied, “I believe it probably does.” The district court then inquired of defense counsel whether that was the conviction he had earlier referenced, defense counsel stated: “That’s the one, your Honor,” and later affirmed that “[t]hat’s the one I was referring to when I said back East, your Honor.” Of course, as we know now, there was no Massachusetts conviction.
In sum, the change-of-plea hearing began with an extensive discussion of how criminal history would affect the imposition of a sentence under the Sentencing Guidelines, and concluded with everyone agreeing that a mandatory minimum sentence was proper based on a non-existent conviction. Under these circumstances, it is quite difficult to conclude that the Spanish-speaking, illiterate defendant, who had never seen a graph before, was making an informed decision.
At the sentencing hearing, confusion again prevailed. The district court once again conducted a thorough Sentencing Guideline analysis, and entertained a defense argument for downward adjustments, all of which would be irrelevant in a mandatory minimum case. After considering the arguments of counsel, the district court was just beginning to impose a sentence within the Guideline range of 70-87 months, when defense counsel interrupted to explain that he thought the sentence should be longer, based on the mandatory minimum requirement. The colloquy is instructive:
THE COURT: (continuing) That will therefore put him in a criminal history category of 3 and a offense level, total offense level of 25, which makes him vulnerable to a sentence of 70 to 87 months. The parties have not agreed on a particular sentence.
DEF. ATT.: Your Honor.
THE COURT: Yes.
DEF. ATT.: I’m sorry to interrupt. He does have a previous conviction, so I think—
*952[colloquy with interpreter omitted]
THE COURT: Yeah, he was in a criminal history category of 3?
DEF. ATT.: No, I’m thinking that it’s a mandatory 10 years—
THE COURT: Oh, is it?
DEF. ATT: I think it—
PROSECUTOR: We’d — I’d have to check the statute, but there would be a statutory minimum due to the existence of the prior.
THE COURT: And the prior was a drug prior?
DEÍ1 ATT.: Yes, it was.
PROSECUTOR: Yes, and we filed an information on that, Your Honor.
THE COURT: Okay, so then it’s the 121 months.
In short, the district court did not proceed at sentencing as though a mandatory minimum sentence applied, and appeared surprised when defense counsel interrupted to suggest that his client should do more time than the district court was contemplating. Asked whether a mandatory minimum might be applicable, the government’s counsel’s said he would “have to check the statute.”
Given this general confusion even among counsel and the district court at both the change-of-plea hearing and the sentencing, it is difficult to believe that Severino was making an informed choice at his change-of-plea hearing, which is the central point of the notice requirements of § 851(a).
Indeed, the plain fact is that if the mandatory minimum sentence had not been required in this case, the district court would have likely imposed a lighter sentence. The district court initially had been poised to impose a sentence within the 70 to 87 months range, and also noted at re-sentencing:
Now, as I mentioned a moment ago, in fairness to Mr. Severino, if I did have discretion, if the 10-year mandatory minimum was not in effect, then there’s no question the Court would give him a better sentence.
B
The second reason that the government’s failure to serve Severino is important in this case is that § 851(a) is not merely a procedural statute, the violation of which might lend itself to an examination under a plain error analysis. See, e.g., United States v. Vonn, 535 U.S. 55, 122 S.Ct. 1043, 1054, 152 L.Ed.2d 90 (2002). Rather, Congress specifically crafted § 851(a) to deny the federal courts the power to enhance a sentence unless the procedural requirements were met.3 Not *953only do courts lack power to impose sentences in excess of statutory authority, United States v. Doe, 53 F.3d 1081, 1083-84 (9th Cir.1995), but the imposition of a sentence in excess of statutory authority constitutes plain error. United States v. Guzman-Bruno, 27 F.3d 420, 423 (9th Cir.1994). Thus, if the procedural requirements of § 851(a) are not satisfied, the district court has no authority to impose an enhanced sentence, and the imposition of such a sentence would constitute plain error.4
A brief review of the legislative history underscores this point. The § 851(a) procedure — and the penalty prescribed for failure to follow it — is in “sharp contrast” with its predecessor statute. United States v. Olson, 716 F.2d 850, 853 (11th Cir.1983). Prior to 1970, federal law required the United States Attorney, in a drug case, to advise the court after conviction but before sentencing whether the defendant was a recidivist and therefore subject to a mandatory enhanced sentence. 26 U.S.C. § 7237(c)(2) (1964). The prior law was based on a mandatory minimum sentencing scheme under which prosecuto-rial discretion did not play a role. As the Fifth Circuit described it:
The thrust of prior law, which required minimum sentences, was mandatory enhancement. The United States attorney was required to advise the court whether the defendant was a first offender. The court was required to enhance the sentence of a multiple offender, whether or not the prosecutor or the court thought enhancement was desirable or necessary.
United States v. Noland, 495 F.2d 529, 532 (5th Cir.1974).
Under the prior statute, prosecutors had no choice in deciding whether to seek enhanced sentences based on prior convictions: the statute required the courts to impose sentence enhancement. Accordingly, notifying the defendant of the prosecutor’s intent would have been superfluous.
Consistent with -the theory of mandatory mínimums, the prior statute was also “silent ... as to the consequences of non-filing of the information prior to imposition of sentence.” United States v. White, 980 F.2d 836, 846 (2d Cir.1992) (Kearse, J., dissenting). It was “in this context of congressionally ordained mandatory enhancement that prior cases upheld enhanced sentences despite procedural defects which did not infringe the defendant’s right to deny and litigate his status.” Noland, 495 F.2d at 533. Accordingly, a number of circuits held under the prior law that the government’s failure to timely file an information seeking sentence enhancement was harmless error. See, e.g., King v. United States, 346 F.2d 123, 124 (1st Cir.1965); United States v. Bell, 345 F.2d 354, 357 (7th Cir.1965); United States v. Duhart, 269 F.2d 113, 116 (2d Cir.1959); Knight v. United States, 225 F.2d 55, 57 (9th Cir.1955).
*954The Comprehensive Drug Abuse Prevention and Control Act of 1970, 21 U.S.C. §§ 801-971, (“the Act”) radically altered existing law and procedure. The “one major goal of the Act was to make more flexible the penalty structure for drug offenses.” Noland, 495 F.2d at 532-33. “The purpose was to eliminate ‘the difficulties prosecutors and courts have had in the past arising out of minimum mandatory sentences.’ ” Id. at 533 (quoting H. Rep. No. 91-1444, 1970 U.S. Code Cong. & Admin. News, pp. 4566, 4576). The theory of the Act was to eliminate mandatory sentences and to invest prosecutors with discretion as to whether to seek enhanced sentences and which prior convictions to invoke. Id. Thus, the statutory scheme was completely everted: Rather than requiring courts to impose mandatory míni-mums regardless of prosecutorial desire, courts were prohibited from enhancing sentences unless the government had timely filed an information stating that it intended to seek an enhanced sentence based on specific prior convictions.
In contrast to the prior statute’s silence about procedural error, the Act specifically addressed the issue. Section 851 provides a remedy for “clerical mistakes,” which may be corrected by filing an amended information prior to the pronouncement of sentence. 21 U.S.C. § 851(a)(1). However, significantly, the Act did not allow the court to excuse or to allow waiver of a failure by the government to timely file an information identifying the crimes. The Act only allows the court to “postpone the trial or the taking of the plea of guilty for a reasonable period” and only then “[u]pon a showing by the United States attorney that facts regarding prior convictions could not with due diligence be obtained prior to trial or before entry of a plea of guilty.” Id. Thus, in this case, when uncertainties arose about the content and service of the information at the change-of-plea hearing, the remedy was to postpone the hearing.
The new procedural restrictions are firmly rooted in the theory of the Act, which shifted responsibility from judges to impose Congressionally-mandated' sentences to prosecutors who were to decide whether to seek enhanced sentences. Under the new statutory scheme, “the district court has no authority to exercise or pretermit” the exercise of executive discretion. United States v. Olson, 716 F.2d 850, 853 (11th Cir.1983). Therefore, “[u]n-less and until prosecutorial discretion is invoked and the government files and serves an information as required by § 851, the district court has no power to act with respect to an enhanced sentence; it can no more enhance the sentence than it could impose imprisonment under a statute that only prescribes a fine.” Id. “Harmless' error cannot give the district court authority it does not possess.” Id.
The Act’s limitations on judicial authority are founded on the separation of powers in two respects: (1) the power of Congress to define criminal sentences; and (2) the power of the executive branch to control prosecutions. As to the power of Congress, it is “indisputable” that “the authority to define and fix the punishment for crime is legislative.” Ex parte United States, 242 U.S. 27, 42, 37 S.Ct. 72, 61 L.Ed. 129 (1916). It is by legislative action that crimes and criminal procedure are defined: a court has no power to impose a sentence in excess of statutory authority. See United States v. Doe 53 F.3d 1081, 1083-84 (9th Cir.1995).
By granting the executive branch discretion to decide whether a sentence enhancement should be sought, the Act concomitantly removed that authority from the judiciary. Just as courts cannot commit an unindicted person to prison, courts cannot enhance a sentence under § 851 until the government elects formally to proceed. Olson, 716 F.2d at 853. In this' context, to *955allow courts to impose a sentence without the valid exercise of executive discretion violates separation of powers. As we have previously observed, “separation of powers concerns prohibit us from reviewing a prosecutor’s charging decisions absent a prima facie showing that it rested on an impermissible basis, such as gender, race or denial of a constitutional right.” United States v. Palmer, 3 F.3d 300, 305 (9th Cir.1993). Indeed, absent such a showing, “we have no jurisdiction to review prosecutors’ charging decisions .... ” United States v. Oakes, 11 F.3d 897, 899 (9th Cir.1993). Until the executive branch validly exercises its option under the Act to seek a sentence enhancement, the courts are powerless to impose one.
Thus, as a matter of statutory construction, it is clear that Congress intended to alter the prior procedures and to impose non-waivable, mandatory requirements. “When Congress acts to amend a statute, we presume it intends its amendment to have real and substantial effect.” Stone v. INS, 514 U.S. 386, 397, 115 S.Ct. 1537, 131 L.Ed.2d 465 (1995). We also presume that when Congress amends a statute, it is knowledgeable about judicial decisions interpreting the prior legislation. United States v. Hunter, 101 F.3d 82, 85 (9th Cir.1996). Further, “a particular statutory provision must be read in context with a view to its place in the statutory scheme.” Gorbach v. Reno, 219 F.3d 1087, 1093 (9th Cir.2000). Finally, and perhaps most importantly, we generally presume that “Congress ‘says in a statute what it means and means in a statute what it says there.’ ” Hartford Underwriters Ins. Co. v. Union Planters Bank, N.A., 530 U.S. 1, 6, 120 S.Ct. 1942, 147 L.Ed.2d 1 (2000) (quoting Conn. Nat. Bank v. Germain, 503 U.S. 249, 254, 112 S.Ct. 1146, 117 L.Ed.2d 391 (1992)). Given the plain language of § 851(a), its structure (namely, the specific remedies provided for procedural violations), the substantive alteration from pri- or law, and the import of judicial construction, there is no doubt that Congress meant what it said in providing that no person could be subjected to enhanced penalties based on prior convictions unless the government timely filed and served an information identifying the convictions upon which it intended to rely. For this reason, a violation of the procedures required by § 851(a) cannot be treated as procedural aberrations subject to a Vonn analysis.
In this case, the government’s failure to comply with the service provisions of § 851(a) deprived the district court of the authority to impose an enhanced sentence. In exceeding its statutory sentencing power, the district court necessarily committed plain error and vacation of the sentence is required.
For these reasons, I respectfully dissent.
. The statute reads in full: "No person who stands convicted of an offense under this part .shall be sentenced to increased punishment by reason of one or more prior convictions, unless before trial, or before entry of a plea of guilty, the United States attorney files an information with the court (and serves a copy of such information on the person or counsel for the person) stating in writing the previous convictions to be relied upon.” 21 U.S.C. § 851(a).
. As the majority properly notes, the district court also erred in this case by not informing Severino, as required by § 851(b), "that any challenge to a prior conviction which is not made before sentence is imposed may not thereafter be raised to attack the sentence.” However, in contrast to § 851(a), Congress did not condition judicial sentencing power on procedural compliance with § 851(b). Therefore, unlike § 851(a) procedural defects, a claim that the district court failed to comply with § 851(b) is subject to plain error review. *951However, because Severino could have maintained a successful challenge to the erroneous information, he would still be entitled to relief on account of the § 851(b) errors.
. The vast majority of circuits have concluded that Congress has established an absolute, non-waivable mandate that bars courts from enhancing sentences under § 851(a) unless the government has complied with its requirements. See, e.g., United States v. Layne, 192 F.3d 556, 575 (6th Cir.1999), cert. denied, 529 U.S. 1029, 120 S.Ct. 1443, 146 L.Ed.2d 330 (2000) ("The requirement is mandatory, and a district court cannot enhance a defendant's sentence based on a prior conviction unless the government satisfies the requirement.”) (citing United States v. Williams, 899 F.2d 1526, 1529 (6th Cir.1990)); Harris v. United States, 149 F.3d 1304, 1306 (11th Cir.1998) ("The Eleventh Circuit and its predecessor court have unambiguously and repeatedly held that a district court lacks jurisdiction to enhance a sentence unless the government strictly complies with the procedural requirements of § 851(a).”); United States v. Kennedy, 133 F.3d 53, 59 (D.C.Cir.1998) ("Put succinctly, ‘[a] prosecutor's compliance with § 851(a)(1) is simply a necessary condition to a judge’s imposing an enhanced sentence on the basis of a defendant’s prior convictions.' ") (quoting United States v. Vanness, 85 F.3d 661, 663 n. 2 (D.C.Cir.1996)); United States v. Steen, 55 F.3d 1022, 1025 (5th Cir.1995) ("If the prosecution fails to comply with § 851’s procedural requirements, a district court cannot enhance a defendant's sentence.”); United States v. Gonzalez-Lerma, 14 *953F.3d 1479, 1485 (10th Cir.1994) ("Failure to file the information prior to trial deprives the district court of jurisdiction to impose an enhanced sentence.") (quoting United States v. Wright, 932 F.2d 868, 882 (10th Cir.1991)); Neary v. U.S., 998 F.2d 563, 565 (8th Cir.1993) ("the statute prohibits an enhanced sentence unless the government first seeks it by properly filing an information prior to trial .... ”); but see Prou v. United States, 199 F.3d 37, 45 (1st Cir.1999) (prosecution's failure to timely file § 851(a) information does not deprive district court of subject-matter jurisdiction).
. For this reason, the question that has occupied a few circuits — whether the requirements of § 851(a) are jurisdictional in nature — is beside the point. If a court imposes a sentence outside the authority granted by Congress, it has committed plain error and reversal is required.