                     FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                       No. 03-10656
                Plaintiff-Appellee,
               v.                                 D.C. No.
                                               CR-03-00650-SMM
JOSE LUIS GONZALEZ-FLORES,
                                                   OPINION
             Defendant-Appellant.
                                           
        Appeal from the United States District Court
                 for the District of Arizona
       Stephen M. McNamee, District Judge, Presiding

                    Submitted April 11, 2005*
                     San Francisco, California

                      Filed August 12, 2005

       Before: Donald P. Lay,** Betty B. Fletcher, and
           Michael Daly Hawkins, Circuit Judges.

              Opinion by Judge Betty B. Fletcher




   *This panel unanimously finds this case suitable for decision without
oral argument. See Fed. R. App. P. 34(a)(2).
   **The Honorable Donald P. Lay, Senior United States Circuit Judge for
the Eighth Circuit, sitting by designation.

                                10491
              UNITED STATES v. GONZALEZ-FLORES          10495


                         COUNSEL

Paul J. Mattern, Phoenix, Arizona, for the defendant-
appellant.

Joan G. Ruffennach, Assistant U.S. Attorney, Phoenix, Ari-
zona, for the plaintiff-appellee.


                         OPINION

B. FLETCHER, Circuit Judge:

   Defendant-appellant      Jose     Luis     Gonzalez-Flores
(“Gonzalez”) was convicted of alien smuggling for leading a
group of nearly two dozen Mexicans into the United States
across the desert. In this direct appeal, Gonzalez claims that
the evidence was insufficient to support his conviction and
that certain testimony admitted at trial was irrelevant and
unduly prejudicial. Gonzalez also attacks his sentence on
Booker grounds; the government argues in response that he
waived his Sixth Amendment rights.
10496           UNITED STATES v. GONZALEZ-FLORES
   We hold that the evidence was sufficient to support the
conviction and that the error arising from the admission of the
prejudicial testimony was harmless, and therefore we affirm
the conviction. However, we reject the government’s conten-
tion that Gonzalez waived his Sixth Amendment rights when
his attorney moved to exclude the prejudicial testimony. We
therefore remand the case pursuant to United States v. Ame-
line.

                      I.   BACKGROUND

   Gonzalez was convicted on one count of bringing in illegal
aliens in violation of 8 U.S.C. § 1324(a)(1)(A)(i). The follow-
ing facts emerged at trial:

   In late May 2003, a group of twenty-three Mexican nation-
als set out on foot from Mexico across the desert into the
United States. Three members of the group were detained by
a border patrol agent on a road near Interstate 8 in Arizona;
these individuals told the agent that there were approximately
twenty other members of their group still in the desert. A
search and rescue operation was initiated, and border patrol
agents found nineteen members of the group in the desert.
Two teenage girls from the group were suffering from severe
heat exhaustion and respiratory problems and were airlifted to
a hospital. Another agent, responding to a report of an illegal
alien, encountered and detained Gonzalez at a barn off I-8
near Yuma, Arizona.

   Three members of the group, Miguel Gonzalez-Flores (no
relation to defendant), Eduardo Salinas-Zagal, and Everardo
Salinas-Zagal (Eduardo’s brother), were detained as material
witnesses and deposed on videotape two weeks after the cross-
ing.1 Gonzalez’s lawyer cross-examined the witnesses in the
videotaped depositions.
  1
   To avoid confusion, we refer to the deposed witnesses by their first
names.
               UNITED STATES v. GONZALEZ-FLORES            10497
   The videotapes of the three depositions were played for the
jury. All three witnesses testified that they were Mexican
nationals and that, led by the defendant, they had crossed the
border other than at a port of entry. Miguel met the two broth-
ers at a border town in Mexico, and they discussed hiring a
guide to help them walk across the border. They then met
Gonzalez, who indicated that he knew the way through the
desert, and so they went with him. They expected to pay Gon-
zalez for being their guide.

  Gonzalez led a group of nearly two dozen people — includ-
ing Miguel, Eduardo, and Everardo — through the desert and
across the border. The group spent a full night and half a day
walking in the desert. At some point during the trek, the group
ran out of water, and Gonzalez left the group to go look for
some. Sometime thereafter, border patrol agents found the
group.

   The initial indictment charged that Gonzalez placed lives in
jeopardy in connection with the offense. Noting that any inju-
ries to members of Gonzalez’s group would not go to an ele-
ment of the crime of bringing in aliens, the court questioned
the parties prior to trial as to the propriety of including this
fact in the indictment. Gonzalez’s lawyer argued: “Since it’s
only a sentencing issue, I don’t think we should concern the
jury with it. . . . I don’t believe it should be included in the
indictment or brought to their attention or have them in any
way find anything about it.” Gonzalez himself made no state-
ment on the matter. The court ruled that the matter of the
harm to others was a sentencing issue and not an element;
consequently, evidence of the injuries sustained by individu-
als Gonzalez brought across the border should be presented at
sentencing rather than to the jury at trial.2
  2
   This discussion took place on September 2, 2003, more than nine
months before the Supreme Court decided Blakely v. Washington, 542
U.S. 296 (2004).
10498         UNITED STATES v. GONZALEZ-FLORES
   Just before the commencement of the trial, however, the
court revisited the subject of the group members’ injuries.
Gonzalez’s lawyer asked the judge to confirm that no testi-
mony as to the two girls’ heat stroke would be permitted and
suggested he would stipulate to the injuries, if necessary, at
sentencing. The government responded that the girls’ distress
“was an important part of the event, and it’s certainly relevant
with respect to sentencing issues.” The court ruled: “I don’t
want to get too far afield if that’s not an element of the
offense, if it’s a sentencing issue. But I think the government
is entitled to some latitude . . . and I’m going to allow [the
government] to get into some of that evidence, about the
results of what happened. So your objection’s overruled.”

   During the trial, a border patrol agent described finding the
two girls, who needed “immediate medical care, advanced
medical care.” The agent characterized the cause of the medi-
cal distress as “[h]eat exhaustion turning into heatstroke.”
According to the agent, during the helicopter flight to the hos-
pital, one of the girls stopped breathing and required resusci-
tation by rescue breathing.

   At the close of the government’s case, the defense moved
for a judgment of acquittal and for a mistrial because the
admission of the evidence of the two girls’ heat stroke vio-
lated Federal Rules of Evidence 402, 403, or both. The court
denied both motions. As to the mistrial motion, the court
explained that the testimony in question “helps to explain the
circumstances of the other testimony of why [Gonzalez] left
to find water and to determine whether he was in fact assist-
ing in bringing people into the United States.” Additionally,
the court didn’t “believe it was so prejudicial.”

   Gonzalez presented no defense; the jury convicted him.
Reiterating the evidentiary argument about the two girls’ heat
stroke (among other arguments), Gonzalez moved for a new
trial. The court denied the motion, once again finding that the
               UNITED STATES v. GONZALEZ-FLORES             10499
probative value of the heat stroke testimony outweighed any
possible prejudicial value.

   The presentence report (PSR) recommended three sentence
enhancements for specific offense characteristics: (1) the
number of aliens smuggled; (2) the fact that Gonzalez brought
people into the desert with insufficient water, thereby reck-
lessly creating a substantial risk of death or serious bodily
injury; and (3) the fact that the two girls suffered severe heat
distress, which constituted serious bodily injury sustained in
connection with the offense. Gonzalez objected to the last of
these enhancements, arguing that the PSR overstated the seri-
ousness of the injuries and as a result added too many levels.
The district court accepted the base offense level from the
PSR, granted a two-level downward departure, and sentenced
Gonzalez to 33 months in prison (the low end of the Guide-
line range), a special assessment of $100, and two years
supervised release.

  Gonzalez timely appealed, and we have jurisdiction pursu-
ant to 28 U.S.C. § 1291.

                        II.   ANALYSIS

A.   Sufficiency of Evidence

   [1] Gonzalez’s sufficiency-of-evidence challenge is easily
rejected, as it rests on the demonstrably erroneous premise
that none of the videotaped depositions that formed the back-
bone of the prosecution’s case was properly admitted into evi-
dence. The record flatly contradicts Gonzalez’s claim: the
trial minutes and the transcript of the trial reveal that all three
tapes were admitted. Gonzalez does not argue, nor could he
plausibly, that the videotaped depositions themselves did not
provide sufficient evidence to sustain his conviction. Gonza-
lez’s sufficiency-of-evidence challenge must fail.
10500           UNITED STATES v. GONZALEZ-FLORES
B.   Evidentiary Error

   Gonzalez argues that the admission of testimony about the
heat stroke suffered by the two girls violated several provi-
sions of the Federal Rules of Evidence. Because we conclude
that the evidence should have been excluded under Rule 403,
which prohibits evidence whose “probative value is substan-
tially outweighed by the danger of unfair prejudice,” we need
not discuss the other rules Gonzalez cites. However, because
we determine that the admission of the unduly prejudicial tes-
timony was harmless, we affirm Gonzalez’s conviction.

1.   Rule 403

   [2] A trial court’s determination that the prejudicial effect
of particular evidence did not substantially outweigh its pro-
bative value under Federal Rule of Evidence 403 is reviewed
for an abuse of discretion. United States v. Plancarte-Alvarez,
366 F.3d 1058, 1062 (9th Cir. 2004). (As to a criminal defen-
dant, “unfair prejudice” refers to “the capacity of some con-
cededly relevant evidence to lure the factfinder into declaring
guilt on a ground different from proof specific to the offense
charged.” Old Chief v. United States, 519 U.S. 172, 180
(1997). In other words, unfairly prejudicial evidence is that
having “an undue tendency to suggest decision on an
improper basis, commonly, though not necessarily, an emo-
tional one.” Id. (citation and internal quotation marks omit-
ted).

  [3] The probative value of evidence against a defendant is
low where the evidence does not go to an element of the
charge. See United States v. Ellis, 147 F.3d 1131, 1135 (9th
Cir. 1998); United States v. Arambula-Ruiz, 987 F.2d 599,
604-05 (9th Cir. 1993). In this case, the government charged
Gonzalez with violating 8 U.S.C. § 1324(a)(1)(A)(i), a crime
with the following elements:

     First, the defendant brought a person who was an
     alien into the United States at a place other than a
               UNITED STATES v. GONZALEZ-FLORES            10501
    designated port of entry or at a place other than as
    designated by a United States immigration official;

    Second, the defendant knew that the person was an
    alien; and

    Third, the defendant acted with the intent to violate
    the United States immigration laws by assisting that
    person to enter the United States at a time or place
    other than as designated by a United States immigra-
    tion official or to otherwise elude United States
    immigration officials.

Ninth Circuit Model Criminal Jury Instructions 9.1 (2003). As
a logical matter, the fact that two girls in Gonzalez’s group
suffered heat stroke does not affect the probability (1) that
Gonzalez brought aliens into the United States other than at
a recognized port of entry, (2) that Gonzalez knew they were
aliens, or (3) that Gonzalez intended to violate U.S. immigra-
tion law by bringing them in. The heat stroke is a mere detail
in the story of the offense. The district court specifically ruled
that the indictment’s reference to the girls’ injuries was sur-
plusage because it was an issue relevant to sentencing rather
than an element of the offense. We agree. Because testimony
about the girls’ heat stroke does not go to any of the elements
of the crime with which Gonzalez was charged, we must con-
sider its probative value low. Ellis, 147 F.3d at 1135;
Arambula-Ruiz, 987 F.2d at 604-05.

   [4] “Where the evidence is of very slight (if any) probative
value, it’s an abuse of discretion to admit it if there’s even a
modest likelihood of unfair prejudice or a small risk of mis-
leading the jury.” United States v. Hitt, 981 F.2d 422, 424 (9th
Cir. 1992). Though the prosecution did not devote a great deal
of time to the girls’ heat stroke, the testimony presented cer-
tainly could have prejudiced Gonzalez unfairly. The border
agent’s description of the young age and dire condition of the
two girls — both of whom needed to be flown to a hospital
10502         UNITED STATES v. GONZALEZ-FLORES
and one of whom required resuscitation by rescue breathing
— very well could have triggered an emotional response from
the jury members, who were likely to be sympathetic to the
girls and consequently want to punish the man who caused
their heat stroke by bringing them into the desert with insuffi-
cient water. Moreover, the prosecution’s closing argument
drove home to the jury the connection, implicit from the testi-
mony, between the actions of Gonzalez and the injuries to the
girls:

    [T]he defendant is the one who told the members of
    the group how much water to bring to try to walk
    across 25 miles of desert in the summer heat in Ari-
    zona. That was perhaps the second most important
    decision they would have to make other than who
    was going to lead them: how much water. You can’t
    survive without water. And the defendant, as the
    leader of the group, told them how much water they
    would need. He was wrong, but he’s the one who
    told them how much to bring.

    ...

    There were people in distress. He was responsible.

We therefore find at least a “modest likelihood of unfair prej-
udice.” Hitt, 981 F.2d at 424.

   [5] The evidence about the two girls’ heat stroke therefore
had “an undue tendency to suggest decision on an improper
basis.” Old Chief, 519 U.S. at 180 (citation and internal quota-
tion marks omitted). The likelihood of unfair prejudice was
high enough to outweigh the minimal proabative value of this
evidence; therefore its admission was an abuse of discretion
under Rule 403.
                 UNITED STATES v. GONZALEZ-FLORES                    10503
2.       Harmless Error
   Where we discover an error not of constitutional magni-
tude, “[w]e must reverse unless there is a ‘fair assurance’ of
harmlessness or, stated otherwise, unless it is more probable
than not that the error did not materially affect the verdict.”
United States v. Morales, 108 F.3d 1031, 1040 (9th Cir. 1997)
(en banc) (citation omitted). The burden to show the harm-
lessness of the error is on the government, and in the rare case
in which we find ourselves in equipoise as to the harmlessness
of the error, reversal is required. See United States v. Seschil-
lie, 310 F.3d 1208, 1214-16 (9th Cir. 2002).3
     3
    In spite of our en banc decision in Morales, we find in our case law
a handful of stray passages reciting the harmless-error rule in an inartful
fashion that reverses the presumptions delineated in Morales by condition-
ing reversal on a showing that the non-constitutional error more likely
than not affected the verdict rather than requiring reversal unless the error
more likely than not did not affect the verdict. See, e.g., United States v.
Verduzco, 373 F.3d 1022, 1032 n.6 (9th Cir. 2004); United States v. Pang,
362 F.3d 1187, 1192 (9th Cir. 2004). Similar distortions have plagued our
precedents concerning harmless error in the civil context. See Obrey v.
Johnson, 400 F.3d 691, 699 (9th Cir. 2005) (observing that “[i]n a some-
what contradictory fashion, . . . we have formulated two variations of the
test for prejudice in civil cases”).
   Fortunately, two fairly recent opinions, one in the criminal context and
one in the civil context, have thoughtfully considered the nature of the
harmless-error inquiry and confirmed that an error presumptively requires
reversal and the burden is on the government to demonstrate otherwise by
showing that the error was more probably than not harmless. See Obrey,
400 F.3d at 699-701; Seschillie, 310 F.3d at 1214-16. In light of the exten-
sive consideration and forceful answers these decisions have given to the
harmless-error question, we feel we are on safe ground in adhering to the
position set forth by our en banc court in Morales (and generally followed
in our case law) and treating as inadvertent the contrary formulations set
out in the following cases since Morales: United States v. Bussell, Nos.
02-50495 & 02-50528, 2005 WL 1620313, at *9 (9th Cir. July 12, 2005);
Verduzco, 373 F.3d at 1032 n.6; Pang, 362 F.3d at 1192; United States v.
Hanna, 293 F.3d 1080, 1085 (9th Cir. 2002); United States v. Nguyen, 284
F.3d 1086, 1089 (9th Cir. 2002); United States v. Angwin, 271 F.3d 786,
798 (9th Cir. 2001); United States v. Jimenez Recio, 258 F.3d 1069, 1087
(9th Cir. 2001); United States v. Edwards, 235 F.3d 1173, 1178 (9th Cir.
2000) (per curiam); United States v. Ciccone, 219 F.3d 1078, 1082 (9th
Cir. 2000); United States v. Hankey, 203 F.3d 1160, 1167 (9th Cir. 2000);
United States v. Hanley, 190 F.3d 1017, 1028 (9th Cir. 1999); United
States v. Ramirez, 176 F.3d 1179, 1182 (9th Cir. 1999).
10504            UNITED STATES v. GONZALEZ-FLORES
    [6] In this case, the government advances no argument that
the evidentiary error was harmless.4 Usually when the govern-
ment fails to argue harmlessness, we deem the issue waived
and do not consider the harmlessness of any errors we find.
See, e.g., United States v. Varela-Rivera, 279 F.3d 1174, 1180
(9th Cir. 2002); United States v. Vallejo, 237 F.3d 1008, 1026
(9th Cir. 2001), amended by 246 F.3d 1150. This approach
makes perfect sense in light of the nature of the harmless-
error inquiry: it is the government’s burden to establish harm-
lessness, and it cannot expect us to shoulder that burden for
it.

   [7] However, we recognize that no interest is served — and
substantial time and resources are wasted — by reversal in
those unusual cases in which the harmlessness of any error is
clear beyond serious debate and further proceedings are cer-
tain to replicate the original result. Fortunately, our precedents
do not foreclose the position that an appellate court’s sua
sponte consideration of harmless error is appropriate on occa-
sions of this type.

   [8] Several of our sister circuits have developed a useful
approach for identifying those extraordinary cases in which an
appellate court should sua sponte consider the harmlessness of
an error it has identified. In an order denying a petition for
rehearing in United States v. Giovannetti, 928 F.2d 225 (7th
Cir. 1991) (per curiam order), the Seventh Circuit considered
the harmless-error waiver question in some detail. The court
recognized that requiring courts to consider harmless error
even where the government has not argued it would be bur-
densome to reviewing courts, which would be obligated to
search through large records without guidance from the par-
  4
   Although the government mentions that a harmless error analysis
applies, it makes no argument on this score nor advances any theory about
how any errors here were harmless. “Issues raised in a brief which are not
supported by argument are deemed abandoned.” Kohler v. Inter-Tel Tech-
nologies, 244 F.3d 1167, 1182 (9th Cir. 2001).
               UNITED STATES v. GONZALEZ-FLORES            10505
ties, and could encourage “salami tactics” by the government,
which could focus its initial briefing exclusively on whether
error has occurred and if it loses, petition for rehearing on the
basis of harmless error. Id. at 226. However, the court also
took note of the potential costs to third parties and to the sys-
tem brought about by needless relitigation of cases in which
the error did not make any difference. Id. at 226-27. Balanc-
ing these considerations, the court adopted the following rule:
“[W]e have discretion to overlook a failure to argue harmless-
ness, and in deciding whether to exercise that discretion the
controlling considerations are the length and complexity of
the record, whether the harmlessness of the error or errors
found is certain or debatable, and whether a reversal will
result in protracted, costly, and ultimately futile proceedings
in the district court.” Id. at 227. Several circuits have followed
or approvingly cited Giovannetti. See United States v. Torres-
Ortega, 184 F.3d 1128, 1136 (10th Cir. 1999); United States
v. McLaughlin, 126 F.3d 130, 135 (3d Cir. 1997); United
States v. Rose, 104 F.3d 1408, 1414 (1st Cir. 1997); Horsley
v. Alabama, 45 F.3d 1486, 1492 n.10 (11th Cir. 1995); Luf-
kins v. Leapley, 965 F.2d 1477, 1481-82 (8th Cir. 1992);
United States v. Pryce, 938 F.2d 1343, 1347-48 (D.C. Cir.
1991) (opinion of Williams, J., announcing the judgment of
the panel); see also United States v. Dolah, 245 F.3d 98, 107
(2d Cir. 2001) (“We have discretion to consider the harmless-
ness of an alleged error even though the Government has not
argued this line of defense.”), abrogated on other grounds by
Crawford v. Washington, 541 U.S. 36, 64 (2004); cf. United
States v. Rodriguez-Preciado, 399 F.3d 1118, 1142-43 (9th
Cir. 2005) (Berzon, J., dissenting in part) (touting the Giovan-
netti approach while noting that the Ninth Circuit has yet to
consider it).

   [9] We find the Seventh Circuit’s analysis persuasive, and
we agree that the government’s failure to argue that an error
is harmless does not categorically preclude our consideration
of that question. We also find helpful the three factors — the
length and complexity of the record, whether the harmless-
10506         UNITED STATES v. GONZALEZ-FLORES
ness of an error is certain or debatable, and the futility and
costliness of reversal and further litigation — that the Seventh
Circuit considers in determining when it is appropriate to rec-
ognize an error’s harmlessness notwithstanding the govern-
ment’s failure to argue it. At the same time, we are
particularly sensitive to the Seventh Circuit’s concerns that
sua sponte consideration of harmlessness will often burden
reviewing courts and give the government too many chances
to argue harmless error. Even more troubling, the practice
may unfairly tilt the scales of justice by authorizing courts to
construct the government’s best arguments for it without pro-
viding the defendant with a chance to respond. See, e.g.,
Stuard v. Stewart, 401 F.3d 1064, 1067 (9th Cir. 2005).

   [10] Mindful of these risks, we believe that while all three
Giovannetti factors are relevant to a court’s determination of
whether to engage in harmless-error review on its own initia-
tive, the second factor — the court’s certainty as to the harm-
lessness of the error — is of particular importance. See
Rodriguez-Preciado, 399 F.3d at 1143 (Berzon, J., dissenting
in part) (“[T]he touchstone of whether courts should reach
harmless error sua sponte is the extent to which the harmless-
ness of the error is open to question.”); Pryce, 938 F.2d at
1348 (opinion of Williams, J., announcing the judgment of the
panel) (“Where the government does not raise the harmless
error issue, I would deem errors ‘harmless’ only where satis-
faction of that standard is beyond serious debate.” (emphasis
in original)); cf. Lufkins, 965 F.2d at 1482 (recognizing harm-
less error sua sponte where “the finding of harmlessness is
beyond reasonable argument”). If the harmlessness of the
error is at all debatable, prudence and fairness to the defen-
dant counsel against deeming that error harmless without the
benefit of the parties’ debate. We agree with the observation
of our colleague from the D.C. Circuit that “where the case
is at all close, defense counsel’s lack of opportunity to answer
potential harmless error arguments may lead the court to miss
an angle that would have shown the error to have been preju-
dicial.” Pryce, 938 F.2d at 1347 (opinion of Williams, J.,
               UNITED STATES v. GONZALEZ-FLORES            10507
announcing the judgment of the panel). We therefore con-
clude that sua sponte recognition of an error’s harmlessness
is appropriate only where the harmlessness of the error is not
reasonably debatable. Since we find this condition satisfied in
Gonzalez’s case, we hold that the evidentiary error we have
identified was harmless and affirm the conviction.

   [11] The record here is small and simple, and we have no
difficulty concluding that allowing the jury to hear testimony
about the girls’ heat stroke was undeniably harmless and that
reversal and further litigation would be futile. Gonzalez’s trial
lasted less than two days, and the evidence against him was
overwhelming. Three witnesses who were part of the group
Gonzalez led across the desert testified that Gonzalez did
exactly what he was charged with doing. The elements of the
crime were easily established. Gonzalez put on no defense.

   [12] We have no doubt that the jury would have convicted
Gonzalez notwithstanding the unduly prejudicial evidence
pertaining to the girls’ heat stroke. The record here does not
merely provide a “ ‘fair assurance’ of harmlessness,” Mora-
les, 108 F.3d at 1040 (citation omitted); it leads us inexorably
to the conclusion that the error’s harmlessness is beyond seri-
ous debate. If we were to send this case back for retrial, the
government would play the same videotaped depositions for
the jury, and the jury would reach the same verdict. We there-
fore hold that the admission of testimony concerning the heat
stroke was harmless, and we affirm Gonzalez’s conviction.

C.   Sentencing Issues

   Gonzalez also claims his sentence is unconstitutional under
United States v. Booker, 125 S. Ct. 738 (2005). Here, Gonza-
lez received three sentence enhancements based on facts
found by the judge under a standard less than beyond a rea-
sonable doubt. These facts were: (1) the number of aliens
smuggled; (2) the fact that Gonzalez brought people into the
desert with insufficient water, thereby recklessly creating a
10508          UNITED STATES v. GONZALEZ-FLORES
substantial risk of death or serious bodily injury; and (3) the
fact that the two girls suffered severe heat distress, which con-
stituted serious bodily injury sustained in connection with the
offense.

   The government claims that Gonzalez waived his Sixth
Amendment rights because the government offered to present
the fact of the heat stroke to the jury and Gonzalez’s lawyer
rejected this offer by urging the court to strike the matter from
the indictment in an (ultimately unsuccessful) attempt to keep
the girls’ heat stroke away from the jury. The government
misapprehends the strict standards for waiver of constitutional
rights generally and for the waiver of the jury trial right in
particular.

  We have recently summarized the principles governing the
waiver of constitutional rights:

    Waiver is the intentional relinquishment or abandon-
    ment of a known right. Courts indulge every reason-
    able presumption against waiver of fundamental
    constitutional rights and do not presume acquies-
    cence in the loss of fundamental rights. Therefore,
    presuming waiver from a silent record is impermissi-
    ble.

United States v. Hamilton, 391 F.3d 1066, 1071 (9th Cir.
2004) (citations, internal quotation marks and source’s alter-
ation marks omitted).

   [13] In particular, we have held that “[t]he right to a jury
trial may only be waived if the following four conditions are
met: (1) the waiver is in writing; (2) the government consents;
(3) the court accepts the waiver; and (4) the waiver is made
voluntarily, knowingly, and intelligently.” United States v.
Duarte-Higareda, 113 F.3d 1000, 1002 (9th Cir. 1997). To
ensure that a waiver is voluntary, knowing, and intelligent, the
district court should:
                UNITED STATES v. GONZALEZ-FLORES              10509
     inform the defendant that (1) twelve members of the
     community compose a jury, (2) the defendant may
     take part in jury selection, (3) a jury verdict must be
     unanimous, and (4) the court alone decides guilt or
     innocence if the defendant waives a jury trial. Fur-
     thermore, the district court should question the
     defendant to ascertain whether the defendant under-
     stands the benefits and burdens of a jury trial and
     freely chooses to waive a jury.

Id. (citation omitted). Though we have declined “to impose an
absolute requirement of such a colloquy in every case,” id. at
1003, in its absence we will find a valid waiver of the jury
trial right only where there are strong indicia that the waiver
was voluntary, knowing, and intelligent. See, e.g., United
States v. Cochran, 770 F.2d 850, 851 (9th Cir. 1985) (finding
waiver of the jury trial right where the defendant discussed
the matter with his lawyer, told the court he wished to waive
the right, and executed a written waiver in the presence of the
court).

   [14] Such indicia are wholly absent from Gonzalez’s case.
The record provides no indication that Gonzalez himself had
considered the nature of the right the government claims his
lawyer waived, or had any idea that his lawyer was waiving
it, much less demonstrated an actual intent to abandon this
right. Gonzalez himself was entirely silent while his counsel
sought to exclude the fact of the two girls’ heat stroke from
the indictment — the act that the government contends
amounted to a waiver of the jury trial right. We will not pre-
sume waiver from a silent record. Hamilton, 391 F.3d at 1071.
Nor will we presume the waiver of one right based on the
assertion of another. See Hays v. Arave, 977 F.2d 475, 477-78
(9th Cir. 1992), overruled on other grounds, Rice v. Wood, 77
F.3d 1138, 1144 n.8 (9th Cir. 1996) (en banc). In the absence
of strong indicia that Gonzalez voluntarily, knowingly, and
intelligently waived his jury trial right, he is entitled to the full
10510            UNITED STATES v. GONZALEZ-FLORES
range of Sixth Amendment protection guaranteed under
United States v. Booker.5

   [15] Because Gonzalez’s sentence was enhanced under a
mandatory-guideline regime based on facts not admitted by
him or proved to a jury beyond a reasonable doubt, his Sixth
Amendment right to a jury trial was violated. Booker, 125
S. Ct. at 749-50. Although Gonzalez did not waive this right,
he did not raise the Sixth Amendment objection at sentencing.
We review unpreserved Booker violations for plain error.
United States v. Ameline, 409 F.3d 1073, 1078 (9th Cir. 2005)
(en banc). Here, though there was error, and it was plain, the
third prong of the plain-error inquiry — whether the error
affected Gonzalez’s “substantial rights” — is in doubt,
because “it is not possible to reliably determine from the
record whether the sentence imposed would have been materi-
ally different had the district court known that the Guidelines
were advisory.” Id. at 1084. Therefore, in accordance with
United States v. Ameline, we remand so that the district court
may answer this question and, if necessary, resentence Gonza-
lez in a manner consistent with Booker and Ameline. See id.
at 1084-85. Gonzalez may, of course, opt out of such resen-
tencing by promptly notifying the district court of his desire
to do so. Id. at 1084.

                       III.   CONCLUSION

   The evidence was sufficient to support the conviction. Tes-
timony pertaining to the heat stroke suffered by two members
of the party Gonzalez led across the desert was unduly preju-
  5
   Our analysis of the waiver question is unaffected by our recent deci-
sion in United States v. Cardenas, 405 F.3d 1046 (9th Cir. 2005), in which
we rejected a defendant’s claim that his waiver of the right to appeal his
sentence was rendered involuntary and unknowing by the Supreme
Court’s subsequent decision in Booker. Id. at 1048. Gonzalez’s claim is
not that the change in law retroactively undermined the voluntariness of
an otherwise-effective waiver; rather, he claims that he did not intend to
waive any right to begin with.
               UNITED STATES v. GONZALEZ-FLORES            10511
dicial, and the district court abused its discretion by admitting
it. However, from our review of this uncomplicated record,
we find it to be beyond debate that the error was harmless and
that reversal and retrial would be futile. Therefore we affirm
Gonzalez’s conviction.

   Gonzalez did not waive his Sixth Amendment rights when
his lawyer tried to keep evidence of the heat stroke away from
his jury. Although Gonzalez was sentenced in violation of the
Sixth Amendment, he did not object in the district court and
therefore we review for plain error. Because we cannot
answer the plain error question on this record, we remand in
accordance with United States v. Ameline.

  AFFIRMED IN PART; REMANDED.
