                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,             
                Plaintiff-Appellee,        No. 04-30082
               v.                            D.C. No.
ARMANDO LABRADA-BUSTAMANTE,               CR-03-02098-EFS
             Defendant-Appellant.
                                      

UNITED STATES OF AMERICA,             
                Plaintiff-Appellee-
                  Cross-Appellant,         Nos. 04-30159
                                      
                                                04-30189
               v.
                                              D.C. No.
CATALINO BARANDA-GALLARDO,                CR-03-02099-EFS
             Defendant-Appellant-
                   Cross-Appellee.
                                      

UNITED STATES OF AMERICA,                 No. 04-30175
                Plaintiff-Appellee,
               v.                            D.C. No.
                                          CR-03-02097-EFS
ROBERTO DUARTE-CRUZ,
                                             OPINION
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
         for the Eastern District of Washington
        Edward F. Shea, District Judge, Presiding

                   Argued and Submitted
            April 4, 2005—Seattle, Washington

                 Filed November 10, 2005

                           15259
15260     UNITED STATES v. LABRADA-BUSTAMANTE
    Before: Ronald M. Gould, Richard C. Tallman, and
          Johnnie B. Rawlinson, Circuit Judges.

              Opinion by Judge Rawlinson
15264       UNITED STATES v. LABRADA-BUSTAMANTE
                         COUNSEL

Nicholas Marchi, Carney & Marchi, P.S., Kennewick, Wash-
ington, for appellant Armando Labrada-Bustamante.

James E. Egan, Kennewick, Washington, for appellant
Roberto Duarte-Cruz.

Sam Swanberg, Law Offices of Sam Swanberg, Kennewick,
Washington, for appellant/cross-appellee Catalino Baranda-
Gallardo.

K. Jill Bolton, Assistant United States Attorney, Yakima,
Washington, for appellee/cross-appellant United States of
America.


                         OPINION

RAWLINSON, Circuit Judge:

   Defendants Armando Labrada-Bustamante (Labrada),
Roberto Duarte-Cruz (Duarte), and Catalino Baranda-
Gallardo (Baranda) were convicted by a jury in the United
States District Court for the Eastern District of Washington of
conspiracy to distribute a controlled substance, methamphet-
amine (meth), in violation of 21 U.S.C. § 846. After determin-
ing that the quantity of meth involved in the proposed sale
was five pounds, the court sentenced both Labrada and Duarte
to 151-month terms of imprisonment. Baranda was sentenced
to a term of 87 months. The defendants appealed, and the
government cross-appealed Baranda’s sentence. We have
jurisdiction pursuant to 28 U.S.C. § 1291. For the reasons dis-
cussed below, we affirm the convictions, vacate the sentences,
and remand to the district court for re-sentencing.
            UNITED STATES v. LABRADA-BUSTAMANTE        15265
                       I
         FACTS AND PROCEDURAL HISTORY

   In February of 2003, Drug Enforcement Agent Alonzo
Garza was contacted by an informant, who indicated that an
individual in Phoenix, Arizona, was willing to bring approxi-
mately forty pounds of meth to Yakima, Washington. Agent
Garza traveled to Phoenix and met with Jesus Martin Ter-
razas, who stated that he could supply the amount of meth
through a man named Roberto. Terrazas then introduced
Agent Garza to Duarte and Labrada.

   Labrada told Agent Garza that he could supply the forty
pounds of meth, but, because the two did not know each
other, he preferred to start with five pounds. Labrada quoted
Agent Garza a price of $12,000 per pound—more expensive
than the meth in Yakima because, according to Labrada, it
was pure and coming directly from Mexico. Labrada also
stated that Agent Garza could “cut it up to four times,” mak-
ing four pounds out of one.

   Terrazas was subsequently arrested in Yakima during a
meth transaction not involving Labrada or Duarte. Choosing
to cooperate with the government, he contacted Duarte on
behalf of Agent Garza to arrange a delivery of meth to Garza
in Yakima. Agent Garza and Duarte spoke several times to
discuss the delivery of the five pounds of meth. Duarte told
Agent Garza during one conversation that he could provide
him with ice methamphetamine (ice) as well. They agreed that
one pound of ice would be delivered in addition to the five
pounds of meth. Although delivery was arranged, the drug
deal was never consummated. The two sides lost contact until
Duarte phoned Agent Garza to inquire whether Agent Garza
was still interested in buying the meth. When Agent Garza
replied that he was, the sale of five pounds of meth for
$12,000 was again agreed upon.

  Duarte called Agent Garza again because, according to
Duarte, his “source” wanted to talk. Agent Garza identified
15266        UNITED STATES v. LABRADA-BUSTAMANTE
that source as Labrada. Labrada indicated that he had a
“hand” and “five fingers”—drug lingo for five pounds of
product. Duarte and Labrada drove to Las Vegas to pick up
Baranda, who then drove the three to Portland, Oregon. From
Portland, Duarte contacted Agent Garza to negotiate a meet-
ing locale. Agent Garza, Duarte, and Labrada eventually met
at a Denny’s in Union Gap, Washington. Baranda remained
in a motel room rented by the defendants.

  During the meeting, possible future transactions were dis-
cussed, and Labrada asked Agent Garza if the agent could
supply a car with Washington plates equipped with a hidden
compartment. The discussion eventually shifted to how the
present transaction would be finalized. Labrada assured Agent
Garza that he would not abscond with the money, even offer-
ing to be held by Agent Garza for ransom. After numerous
unsuccessful attempts to reach mutually agreeable terms, the
meeting concluded. Even as they were leaving, however,
Labrada attempted to consummate a deal. He told Agent
Garza that there was more meth in Phoenix and that if things
went well, he could simply make a call and the product would
be brought up to Yakima.

   After the meeting concluded, the Drug Enforcement
Administration (DEA) instructed the Washington State Patrol
to stop defendants’ car.1 DEA Agent Meliton Rodriguez, the
local agent overseeing the investigation and undercover oper-
ation, arrived on the scene a few minutes after the stop. Agent
Rodriguez, a native Spanish speaker, individually advised
each defendant of his Miranda2 rights in Spanish using a DEA
Form 13A.3 Duarte and Labrada said nothing in response
except that they understood their rights. In response to Agent
Rodriguez’s suggestion that he knew Duarte and Labrada
  1
    By this time, Baranda had reunited with Duarte and Labrada.
  2
    Miranda v. Arizona, 384 U.S. 436 (1966).
  3
    A DEA Form 13A states the Miranda warnings in both English and
Spanish.
            UNITED STATES v. LABRADA-BUSTAMANTE          15267
were in Yakima to sell meth, Baranda asked, “[d]id you ever
think that there might be another car involved?” Baranda con-
sented to a search of the vehicle; no drugs or weapons were
found.

   The defendants were taken to the DEA offices in Yakima,
where Rodriguez separately interviewed each one. During
questioning, Baranda admitted that he knew he was going to
Washington to be involved in a drug deal. Duarte did not
respond when told that the DEA knew he was involved in a
drug deal. However, when asked if it was his intent to simply
steal the money from Agent Garza, Duarte responded that it
was not. Labrada admitted to Agent Rodriguez that he was in
Yakima to do a drug deal with Agent Garza. When asked
about the location of the meth, Labrada indicated that it was
with a man named Ernesto, the source supplier of meth in
Yakima. However, Ernesto was never located.

   Duarte, Labrada, and Baranda were charged with one count
of conspiracy to distribute a controlled substance in violation
of 21 U.S.C. § 846. Labrada filed a motion to suppress state-
ments made by him to Agent Rodriguez, which Duarte joined.
At the suppression hearing, Agent Rodriguez testified that he
read the Miranda warnings to each defendant, in Spanish and
using a DEA Form 13A. He further testified that before ques-
tioning the defendants, he reminded them of their rights, sum-
marized those rights, and asked them whether they understood
those rights. Each defendant indicated that he did. No threats
or promises were made to any of the defendants during the
interviews.

   Agent Gilliam, who was present during the interviews, cor-
roborated Agent Rodriguez’s testimony. Agent Gilliam testi-
fied that no defendant expressed any confusion about what
those rights meant. The district court specifically found that
Agent Rodriguez read each defendant his rights at the initial
stop, summarized those rights at the station, and elicited a
response that each defendant understood his rights. After con-
15268         UNITED STATES v. LABRADA-BUSTAMANTE
sidering the totality of the circumstances, the court ruled that
the defendants’ statements were voluntary, and the motion to
suppress was denied.

   After a three-day jury trial, the defendants were convicted
as charged. For sentencing purposes, the court used the agreed
upon amount of meth—five pounds—resulting in a base
offense level of 34 and a sentence range of 151 to 188
months. U.S. Sentencing Guidelines Manual (USSG)
§ 2D1.1(c)(3) (2002).4 Labrada and Duarte were each sen-
tenced to 151-month terms of imprisonment. Baranda was
sentenced to 87 months in prison after the court sustained
Baranda’s collateral challenge to the California felony drug
conviction used to calculate Baranda’s criminal history score.

   Labrada now challenges the district court’s denial of his
motion to suppress and his Rule 29 motion based on the suffi-
ciency of the evidence. He also contends that he received
ineffective assistance of counsel during sentencing and that
the district court violated his Sixth Amendment rights by sen-
tencing him based on a quantity of meth not found by the jury
beyond a reasonable doubt. Duarte similarly challenges the
denial of the motion to suppress and the district court’s drug
quantity determination. Duarte also contends that the “safety
valve” factors under 18 U.S.C. § 3553(f) are unconstitutional
because their consideration requires findings of fact by the
district court and not a jury. Finally, Baranda challenges his
sentence because it is based upon a factual finding, the quan-
tity of meth, made by the district court and not a jury.

   The government cross-appeals Baranda’s sentence on the
basis that the district court erred in allowing Baranda to col-
laterally challenge his prior conviction.
   4
     It appears that the defendants were sentenced using the 2002 version
of the Guidelines. However, this section is the same in the 2002, 2003, and
2004 versions of the United States Sentencing Guidelines. See USSG
§ 2D1.1(c)(3) (2002); USSG § 2D1.1(c)(3) (2003); USSG § 2D1.1(c)(3)
(2004).
             UNITED STATES v. LABRADA-BUSTAMANTE         15269
                           II
                       DISCUSSION

  A.     Labrada-Bustamante

    1.    Motion to suppress

   Labrada challenges the district court’s denial of his motion
to suppress, asserting that he could not have voluntarily or
knowingly waived his rights because, as a Mexican national,
he was not familiar with the United States’ justice system and
did not understand what his rights meant.

   A decision on a motion to suppress is reviewed de novo.
United States v. Charley, 396 F.3d 1074, 1079 (9th Cir.
2005). “We review the voluntariness of a waiver of Miranda
rights de novo.” United States v. Younger, 398 F.3d 1179,
1185 (9th Cir. 2005) (citation omitted). “Whether the decision
was knowing and intelligent is reviewed for clear error.” Id.
(citation omitted).

   [1] The validity of a Miranda waiver depends on the total-
ity of the circumstances and whether the defendant “was
aware of the nature of the right being abandoned and the con-
sequences of the decision to abandon it.” Id. (citation and
internal quotation marks omitted).

   The district court credited Agent Rodriguez’s testimony
that each defendant stated awareness and understanding of his
rights. We give “special deference” to credibility determina-
tions and are “especially reluctant” to set aside such determi-
nations. United States v. Becerra-Garcia, 397 F.3d 1167,
1172 (9th Cir. 2005) (citations omitted). In addition, Labrada
acknowledged on cross-examination that he understood what
it meant to have the right to remain silent.

  [2] Agent Rodriguez was not required to explain to Labrada
what the Miranda rights meant. The fact that Labrada might
15270       UNITED STATES v. LABRADA-BUSTAMANTE
not be familiar with the United States’ form of justice is
merely one factor to be considered. See, e.g., United States v.
Frank, 956 F.2d 872, 877 (9th Cir. 1991), as amended, (stat-
ing that “[w]hen considering the totality of the circumstances,
relevant factors include age, experience, education, back-
ground and intelligence.”) (citation, internal quotation marks,
and alteration omitted). Considering the totality of the
circumstances—including Agent Rodriguez’s testimony and
Labrada’s admission that he understood his rights—the dis-
trict court’s finding that Labrada knew and understood his
rights is not clearly erroneous.

   [3] Labrada’s Miranda waiver was also voluntary. There
was no evidence in the record of “police overreaching,” and
both agents testified that no threats or promises were made to
any of the defendants. See United States v. Cazares, 121 F.3d
1241, 1244 (9th Cir. 1997) (stating that “the voluntariness of
a waiver has always depended on the absence of police over-
reaching.”) (citation and internal quotation marks omitted).
Therefore, we hold that the district court properly denied
Labrada’s motion to suppress.

    2.   Sufficiency of the evidence

   Labrada contends that because there was no meth ever
found on him or his co-defendants, and because he continu-
ally maintained that his true intent was to steal money, not sell
meth, the evidence was insufficient to support the jury’s find-
ing that he intended to distribute a controlled substance.

   “We review de novo the denial of a motion for a judgment
of acquittal based on the alleged insufficiency of the evi-
dence.” United States v. Pearson, 391 F.3d 1072, 1075 (9th
Cir. 2004) (citation omitted). “[V]iewing the evidence in the
light most favorable to the government, we must determine
whether any rational trier of fact could have found, beyond a
reasonable doubt, the requisite elements of the offense
charged.” Id. (citation omitted).
            UNITED STATES v. LABRADA-BUSTAMANTE            15271
   [4] “To establish a drug conspiracy, the government must
prove: 1) an agreement to accomplish an illegal objective and
2) the intent to commit the underlying offense.” United States
v. Romero, 282 F.3d 683, 687 (9th Cir. 2002) (citation omit-
ted). In this case, the underlying offense was the distribution
of fifty grams or more of meth. Thus, the government was
required to prove that Labrada intended to distribute at least
fifty grams of meth. “Culpable intent can be inferred from the
defendant’s conduct and from the surrounding circum-
stances.” United States v. Bucher, 375 F.3d 929, 934 (9th Cir.
2004) (citations and alteration omitted).

   [5] There was extensive evidence in this case from which
a rational jury could infer that Labrada had the requisite intent
to distribute meth. Agent Garza engaged in extensive negotia-
tions for the sale of meth with both Labrada and Duarte.
Labrada used expressions common in the drug trade and the
defendants drove from Phoenix to Yakima to consummate the
transaction. At the meeting in Washington, Labrada attempted
to negotiate the exchange, even offering to remain with Agent
Garza for ransom until the deal was completed. When negoti-
ations stalled, Labrada persisted in attempting to make the
sale. Finally, Labrada admitted to Agent Rodriguez that he
was in Washington for a drug deal.

   [6] Viewing this evidence in the light most favorable to the
government, and drawing all reasonable inferences against
Labrada, as we must, United States v. Rodriguez, 360 F.3d
949, 955 (9th Cir. 2004), the evidence was sufficient for a
rational jury to find, beyond a reasonable doubt, that Labrada
intended to distribute fifty grams or more of meth.

    3.   Ineffective assistance of counsel

   “Effectiveness of counsel is a mixed question of law and
fact, reviewed de novo.” United States v. Jeronimo, 398 F.3d
1149, 1155 n.3 (9th Cir. 2005) (citation omitted). “[A]s a gen-
eral rule, we do not review challenges to the effectiveness of
15272       UNITED STATES v. LABRADA-BUSTAMANTE
defense counsel on direct appeal.” Id. at 1155 (citation omit-
ted). However, we have developed “two extraordinary excep-
tions to this general rule: . . . (1) where the record on appeal
is sufficiently developed to permit determination of the issue,
or (2) where the legal representation is so inadequate that it
obviously denies a defendant his Sixth Amendment right to
counsel.” Id. at 1156 (citation omitted). The record in this
case is sufficiently developed for us to determine that Labrada
did not receive ineffective assistance of counsel.

   [7] Labrada’s ineffective assistance claim rests on his trial
counsel’s failure to submit written objections to the Pre-
sentence Report (PSR) before sentencing. Although Labrada’s
counsel did fail to submit written objections, he orally
objected to portions of the PSR at the sentencing hearing.
Although the district court stated that the objections should
have been made in writing, it accepted and considered the
objections nonetheless. In fact, the court sustained counsel’s
objection to the two-level obstruction of justice enhancement.
Assuming, without deciding, that counsel’s performance was
deficient, because the court considered the objections,
Labrada cannot make the requisite showing of prejudice, i.e.,
that the result of the proceeding would have been different.
See United States v. Fredman, 390 F.3d 1153, 1156 (9th Cir.
2004) (stating that a defendant must show prejudice to estab-
lish a claim of ineffective assistance of counsel, meaning “that
there is a reasonable probability that, but for counsel’s unpro-
fessional errors, the result of the proceeding would have been
different.”) (citation omitted).

    4.   Quantity of meth for sentencing

   Labrada challenges the district court’s use of five pounds
as the quantity of meth involved in the offense for purposes
of establishing his base offense level. He argues that this find-
ing by the court violated his Sixth Amendment right to have
a jury determine the quantity of drugs beyond a reasonable
doubt. We “review de novo whether the district court violated
            UNITED STATES v. LABRADA-BUSTAMANTE            15273
the constitutional rule articulated in Apprendi.” United States
v. Smith, 390 F.3d 661, 663 (9th Cir. 2004) (citation omitted).

   [8] To comply with the requirements of the Sixth Amend-
ment, “[o]ther than the fact of a prior conviction, any fact that
increases the penalty for a crime beyond the prescribed statu-
tory maximum must be submitted to a jury, and proved
beyond a reasonable doubt.” Apprendi v. New Jersey, 530
U.S. 466, 490 (2000). In Blakely v. Washington, 124 S. Ct.
2531 (2004), the United States Supreme Court explained that
“the statutory maximum for Apprendi purposes is the maxi-
mum sentence a judge may impose solely on the basis of the
facts reflected in the jury verdict or admitted by the defen-
dant.” Id. at 2537 (citations and internal quotation marks
omitted) (emphasis in the original). The Court’s decision in
Blakely applies to the United States Sentencing Guidelines.
See United States v. Booker, 125 S. Ct. 738, 746 (2005).

   [9] Although the jury found the defendants guilty of con-
spiring to distribute only fifty grams or more of methamphet-
amine, Labrada admitted under oath that the amount of meth
involved in the proposed sale was five pounds. Therefore, the
use of five pounds to determine his base offense level violates
neither Apprendi nor Blakely. See id. at 756 (“[W]e reaffirm
our holding in Apprendi: Any fact (other than a prior convic-
tion) which is necessary to support a sentence exceeding the
maximum authorized by the facts established by a plea of
guilty or a jury verdict must be admitted by the defendant or
proved to a jury beyond a reasonable doubt.”) (emphasis
added).

   [10] Despite the lack of a Sixth Amendment violation, we
vacate Labrada’s sentence and remand his case to the district
court for re-sentencing. At Labrada’s sentencing hearing, the
district court expressly advised the parties that the sentence
was beyond his control. He stated, “[T]he kind of penalties
that [the] Congress of the United States has imposed . . . are
very, very severe and I have no control over those. You’re
15274        UNITED STATES v. LABRADA-BUSTAMANTE
facing more than 12 years in prison which is an extraordinar-
ily long time for a first offender on a case where — of a case
involving the kind of behavior that this case involved . . .” In
United States v. Ameline, 409 F.3d 1073, 1084 (9th Cir. 2005)
(en banc), we held that a limited remand is appropriate,
“where it is not possible to reliably determine from the record
whether the sentence imposed would have been materially
different had the district court known that the Guidelines were
advisory . . .” On the other hand, re-sentencing is appropriate
where we can reliably determine from the record that the sen-
tence imposed would have differed materially. See United
States v. Crawford, 422 F.3d 1145, 1146 (9th Cir. 2005). As
Labrada’s case is one of those rare cases where the district
court stated on the record that he felt compelled to impose a
harsher sentence because of the mandatory nature of the
Guidelines, a remand for re-sentencing is appropriate. Id.

  B.     Duarte-Cruz

    1.    Motion to suppress

   Like Labrada, Duarte challenges the voluntariness of his
Miranda waiver. He maintains that his silence at the scene of
the arrest, coupled with Agent Rodriguez’s failure to obtain
an express statement of waiver, demonstrates that he did not
voluntarily waive his rights. However, an express waiver is
not required for a valid Miranda waiver. See, e.g., United
States v. Rodriguez-Preciado, 399 F.3d 1118, 1127 (9th Cir.
2005) (“Waivers of Miranda rights need not be explicit; a sus-
pect may impliedly waive the rights by answering an officer’s
questions after receiving Miranda warnings.”) (citation omit-
ted). Duarte’s acknowledgment that he understood his rights,
and the absence of “police overreaching,” persuade us that
Duarte knowingly and intelligently waived his Miranda rights
and that the waiver was voluntary.
              UNITED STATES v. LABRADA-BUSTAMANTE                   15275
      2.   The “safety valve” provision of 18 U.S.C.
           § 3553(f)

   Duarte challenges the denial of his request for application
of the “safety valve” provision of 18 U.S.C. § 3553(f) to
avoid the ten-year statutory mandatory minimum provided in
21 U.S.C. § 841(b)(1)(A). Duarte does not quarrel with the
district court’s finding that he failed to give a truthful state-
ment about the complete circumstances of the offense.5 Id.
Instead, he claims that the five factors enumerated in section
3553(f) are unconstitutional under Blakely because each
requires a finding by a judge rather than a jury.

   “The constitutionality of a statute is a legal question of law
that we review de novo.” Younger, 398 F.3d at 1192 (citation
omitted). “[A]ny fact that increases the penalty for a crime
beyond the prescribed statutory maximum must be submitted
to a jury, and proved beyond a reasonable doubt.” Apprendi,
530 U.S. at 490 (emphasis added).

   [11] The statutory mandatory minimum sentences under 21
U.S.C. § 841(b) are not triggered unless and until a jury has
found, beyond a reasonable doubt, the quantity of a controlled
substance. See United States v. Velasco-Heredia, 319 F.3d
1080, 1086 (9th Cir. 2003) (stating that after Apprendi, the
statutory mandatory minimum sentences under 21 U.S.C.
§ 841 do not apply “until the jury, or the court in a bench trial,
finds beyond a reasonable doubt [ ] the quantity involved in
the violation.”). Because mandatory minimum sentences
under section 841(b) presuppose a jury’s determination of the
underlying facts, their imposition does not offend either
Apprendi or Blakely. See United States v. Hitchcock, 298 F.3d
  5
     The last of five factors that the sentencing court must find under
§ 3553(f) states, in part, that “not later than the time of the sentencing
hearing, the defendant has truthfully provided to the Government all infor-
mation and evidence the defendant has concerning the offense or offenses
. . . .” 18 U.S.C. § 3553(f)(5) (2000).
15276       UNITED STATES v. LABRADA-BUSTAMANTE
1021 (9th Cir. 2002), as amended, (holding that “mandatory
minimums do not implicate Apprendi.”) (citation omitted).
Duarte would have us hold that facts allowing a decreased
sentence below that mandatory minimum must be found by a
jury beyond a reasonable doubt as well. Neither Apprendi nor
Blakely compel such a holding. Therefore, we hold that the
safety valve provision of 18 U.S.C. § 3553(f) is not unconsti-
tutional under Apprendi or Blakely. However, because the dis-
trict court sentenced Duarte under the then-mandatory
Guidelines, we also vacate his sentence and remand for re-
sentencing. As with Labrada, the district court expressly
lamented the mandated sentence, stating that it was “strug-
gling . . . because it would like to find a way to give [Duarte]
less time.” The court’s statement justifies concluding that the
sentence would have differed materially under advisory
Guidelines. See Ameline, 409 F.3d at 1084.

  C.    Baranda-Galardo

   The only issue raised by Baranda is whether the district
court violated his Sixth Amendment rights by using five
pounds of meth in determining his base offense level. Unlike
Labrada or Duarte, Baranda never made an admission as to
the quantity of meth involved in the proposed sale to Agent
Garza. However, Baranda faced a statutory minimum sen-
tence of twenty years predicated upon the jury’s finding that
the defendants conspired to distribute fifty grams of metham-
phetamine and upon Baranda’s prior drug conviction. As a
result, the court’s attribution of five pounds of meth to
Baranda did not constitute Apprendi error. See Harris v.
United States, 536 U.S. 545, 557, 565 (2002); see also United
States v. Dare, No. 04-30202, 2005 WL 2319653, at *8 (9th
Cir. Sept. 23, 2005) (noting that Booker has no application to
a mandatory minimum sentence and that the outcome of re-
sentencing “could not possibly be different” where a manda-
tory minimum sentence is imposed).
                UNITED STATES v. LABRADA-BUSTAMANTE                    15277
  D.      Government’s cross-appeal

   As noted above, because Baranda had a prior felony drug
conviction, he faced a mandatory minimum sentence of
twenty years. See 21 U.S.C. § 841(b) (1999 & Supp. 2005).
The district court allowed Baranda to collaterally attack the
prior conviction, a decision that we review de novo. See
United States v. Hernandez-Vermudez, 356 F.3d 1011, 1013
(9th Cir. 2004).

   [12] Although a defendant may collaterally attack a prior
conviction used to enhance his sentence,6 no collateral chal-
lenge may be made if the prior conviction is more than five
years old. 21 U.S.C. 851(e).7 The district court allowed
Baranda to attack the conviction for the purpose of computing
criminal history points, and the court sustained the attack. As
a result, Baranda had zero criminal history points, making
him eligible for the “safety valve” provision of 18 U.S.C.
§ 8553(f).8 The court found that Baranda satisfied the “safety
valve” requirements and sentenced him to an 87-month prison
term.
  6
   Such a challenge is made under section 851(c), which states, in part:
      If the person denies any allegation of the information of prior
      conviction, or claims that any conviction alleged is invalid, he
      shall file a written response to the information . . . . The court
      shall hold a hearing to determine any issues raised by the
      response which would except the person from increased punish-
      ment.
21 U.S.C. § 851(c).
   7
     Section 851(e) states that “[n]o person who stands convicted of an
offense under this part may challenge the validity of any prior conviction
alleged under this section which occurred more than five years before the
date of the information alleging such prior conviction.” 21 U.S.C.
§ 851(e). Baranda’s prior conviction was entered on May 22, 1997, and
the government’s information in this case was filed on August 19, 2003.
   8
     The first prerequisite for the “safety valve” provision is that the defen-
dant not have more than one criminal history point. 18 U.S.C.
§ 3553(f)(1).
15278        UNITED STATES v. LABRADA-BUSTAMANTE
   [13] Baranda concedes, as he must, that he could not collat-
erally attack his prior conviction as the district court allowed.
See United States v. Burrows, 36 F.3d 875, 885 (9th Cir.
1994) (holding that a defendant cannot collaterally challenge
a prior conviction used to calculate criminal history points);
see also Clawson v. United States, 52 F.3d 806, 807 (9th Cir.
1995) (concluding that a defendant has “no constitutional
right to collaterally attack the validity of a state conviction in
a federal sentencing hearing on any basis other than denial of
the right to counsel.”) (citation omitted).

   Although acknowledging the district court’s error, Baranda
argues that any sentencing error was harmless because there
was insufficient evidence to prove he was involved in the con-
spiracy. This issue should have been raised in Baranda’s
opening brief and is therefore waived. United States v. Kama,
394 F.3d 1236, 1238 (9th Cir. 2005) (“Generally, an issue is
waived when the appellant does not specifically and distinctly
argue the issue in his or her opening brief.”) (citation omit-
ted). In any event, Baranda’s admission that he went to Wash-
ington to be involved in a drug deal was sufficient evidence
of his involvement in the conspiracy. See United States v.
Alvarez, 358 F.3d 1194, 1201 (9th Cir. 2004) (“When the evi-
dence establishes that a conspiracy exists, there is sufficient
evidence to support a conviction for knowing participation in
that conspiracy if the government is able to establish, beyond
a reasonable doubt, ‘even a slight connection’ between the
defendant and the conspiracy.”) (citations omitted).

   Baranda’s next claim is that the government failed to pro-
vide sufficient proof of his prior conviction. Because Baranda
did not raise this issue in his objections to the PSR or during
his sentencing hearing, review is for plain error. See United
States v. Scrivner, 114 F.3d 964, 966 (9th Cir. 1997) (apply-
ing plain error where defendants did not object to the PSR or
during their sentencing hearing.).
                UNITED STATES v. LABRADA-BUSTAMANTE                    15279
   [14] Before a sentence may be enhanced under 21 U.S.C.
§ 841(b) for a prior drug conviction, the government must file
an information in compliance with 21 U.S.C. § 851(a).9 “The
statute merely ensures proper notice so a defendant is able to
challenge the information . . . .” United States v. Severino,
316 F.3d 939, 943 (9th Cir. 2003) (en banc) (citation and
internal quotation marks omitted). The statute’s purpose of
providing notice is satisfied “[i]f the defendant, reading the
information in context, will have no trouble understanding
which prior conviction the prosecutor means to identify . . . .”
Id. at 943-44.

   [15] The government filed the required information in this
case, identifying the 1997 felony drug conviction used to
enhance Baranda’s sentence. Baranda obviously had no trou-
ble recognizing the conviction because it was the only one
alleged, and he challenged it on the basis that his plea collo-
quy was constitutionally deficient. Therefore, he “could not
have been confused about the prior conviction[,]” and section
851(a) was satisfied. Id. at 944.

   Baranda also raises a constitutional challenge to 21 U.S.C.
§ 851(e) under the equal protection and due process clauses
of the Fifth Amendment. However, we have previously con-
sidered and rejected this very argument. See United States v.
Davis, 36 F.3d 1424, 1438-39 (9th Cir. 1994) (rejecting the
claim that section 851(e) violates due process or equal protec-
tion.).
  9
   Section 851(a) provides, in relevant part:
      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 . . . stating in writing the previous convictions to be
      relied upon . . . .
21 U.S.C. § 851(a).
15280        UNITED STATES v. LABRADA-BUSTAMANTE
  Finally, Baranda maintains that imposition of the twenty-
year mandatory minimum sentence violates the Eighth
Amendment because such a sentence would not reflect an
individualized assessment of his culpability. “We review de
novo the constitutionality of a sentence.” United States v.
Barajas-Avalos, 377 F.3d 1040, 1060 (9th Cir. 2004) (citation
omitted).

   [16] “[F]ederal courts should be reluctant to review legisla-
tively mandated terms of imprisonment because the fixing of
prison terms for specific crimes is properly within the prov-
ince of legislatures, not courts.” Id. (citations, alteration, and
internal quotation marks omitted). For this reason,
“[m]andatory minimum sentencing schemes have been con-
sistently upheld against constitutional challenge,” United
States v. Wilkins, 911 F.2d 337, 339 (9th Cir. 1990) (citing
cases), and “outside the context of capital punishment, suc-
cessful challenges to the proportionality of particular sen-
tences have been exceedingly rare.” Barajas-Avalos, 377 F.3d
at 1060 (citation and alteration omitted).

   [17] In this case, the imposition of the twenty-year manda-
tory minimum sentence would not be cruel and unusual for a
defendant who, like Baranda, has been convicted of a serious
drug crime and has a prior felony drug conviction. See id. at
1060-61 (upholding a 360-month sentence for a defendant
convicted of attempting to manufacture and manufacturing
methamphetamine and who had only a prior misdemeanor
conviction).

   [18] We conclude that the district court erred in allowing
Baranda to collaterally attack his prior conviction, and we
therefore vacate his sentence and remand to the district court
for re-sentencing consistent with this opinion.

                            III
                        CONCLUSION

 The district court correctly denied Labrada and Duarte’s
motion to suppress because both defendants knowingly and
            UNITED STATES v. LABRADA-BUSTAMANTE           15281
intelligently waived their Miranda rights and the waivers
were voluntary. There was sufficient evidence for a rational
jury to find, beyond a reasonable doubt, that Labrada intended
to distribute fifty grams or more of meth. Labrada did not
receive ineffective assistance of counsel, as the court accepted
and considered counsel’s oral objections. Because of the dis-
trict court’s clear indication that it felt constrained by the
Guidelines, and because the district court impermissibly per-
mitted Baranda to collaterally attack his 1997 conviction, we
vacate the sentences imposed so that the defendants can be re-
sentenced under the now-advisory Guidelines.

 CONVICTIONS     AFFIRMED;         SENTENCES
VACATED and REMANDED for re-sentencing.
