CARDAMONE, Circuit Judge:
Three appellants are before us as a result of their convictions arising from their involvement' over several years in the illegal distribution of a huge amount of drugs by forged prescriptions. After the jury returned a guilty verdict on a multicount indictment against one of the appellants, the trial court set aside the verdict as to one count, which prompted the government’s appeal. The resolution of the appeals from the judgments of convictions against appellants is relatively straightforward. What sets this case apart are the problems raised by the government’s appeal.
The confusion began when the district court charged the jury that conspiracy violations and substantive violations attributed to a defendant because of his membership in a conspiracy could not be considered as predicate offenses to support a conviction for operating a continuing criminal enterprise in violation of 21 U.S.C. § 848 (1982). As our recent decision in United States v. Young, 745 F.2d 733 (2d Cir.1984), makes clear, this charge was erroneous. Further, the jury was also directed to return with its verdict answers to certain written interrogatories. With this cautionary stroke, the district judge enabled us to know on what factual basis the jury reached its verdict. Such knowledge is crucial on this appeal because the jury found appellant guilty of those offenses that — despite the trial judge’s charge to the contrary — we held may constitute predicates for a § 848 violation.
This is not therefore a case in which a jury possibly came to its result for an impermissible reason, but rather a situation in which a jury’s sustainable verdict was reached after it acted in disregard of a legally incorrect charge. That is, this is the rare case in which tv/o wrongs do make a right. For us to affirm the setting aside of the conviction — in light of abundant evidence of guilt — would simply compound the wrong. Hence, we reverse the district court’s order and reinstate the guilty verdict.
I
Proceedings Below
Marshall J. Muhammad, Charles Jones, and Raymond Piacente appeal from judgments of conviction after a jury trial in the United States District Court for the Southern District of New York (Lowe, J.). The jury found Muhammad guilty of various narcotics offenses through his arranging the sale, in drugstores with which he was affiliated, of pharmaceutical drugs without the prescriptions required by law. He was convicted of four counts of distribution of narcotics in violation of 21 U.S.C. § 841, conspiracy to violate the narcotics laws of the United States in violation of 21 U.S.C. § 846, and operating a continuing criminal enterprise in violation of 21 U.S.C. § 848. The jury found appellants Jones and Piacente guilty under § 846 of a conspiracy to violate the narcotics laws. Jones was also convicted of four substantive narcotics violations under § 841, and operating a continuing criminal enterprise under § 848.
Appellants raise a number of claims, only two of which require discussion. All of the appellants argue that the district court erred by allowing the government on its direct examination to refer to the truth-telling provisions of the witnesses’ signed cooperation agreements. Jones and Piacente also claim that the presence of two alternate jurors at the onset of the jury deliberations requires reversal of their convictions. The government has appealed contending that the district court erred in setting aside Jones’ conviction on the § 848 charge.
II
Facts
The government’s proof at trial established that between 1976 and 1983 massive [521] amounts of prescription drugs were being dispensed without prescriptions or with forged prescriptions from the Harlem Community Pharmacy (Harlem Pharmacy) in Manhattan and the Liotta, Brownsville, and Established Pharmacies in Brooklyn. The government also proved that prescription drugs ordered for the Greenleaf Clinic in Queens were being diverted to the Harlem Pharmacy. The jury found that Muhammad, Jones, and Piacente were all involved in this illegal drug distribution scheme. Muhammad owned the Harlem Pharmacy and at some time was owner or part owner of the other pharmacies. His office was at the Harlem Pharmacy where he managed the pharmacy section. He also owned the Greenleaf Clinic. Jones managed the non-pharmacy section of the Harlem Pharmacy from 1977 to 1979, and later managed the Liotta Pharmacy. He was also part owner of the Brownsville and Established Pharmacies. Piacente managed the nonpharmacy section of the Liotta Pharmacy.
One of the government’s witnesses at trial was James Stephenson, a United States Drug Enforcement Agent, who testified with respect to audits of the pharmacies and the clinic. His testimony demonstrated that purchases of controlled substances were not balanced by prescription sales, with purchases exceeding sales by a ratio of ten to one. In addition, several unindicted co-conspirators testified for the government. Jean-Marie Joseph was the supervising pharmacist at Harlem Pharmacy in 1977, later he worked part-time at Liotta and Brownsville, and was part owner of Established where he also worked as a pharmacist. Joseph worked at Harlem Pharmacy at a time when Charles Jones managed the nonpharmacy section. Joseph testified that he and others sold controlled substances under forged prescriptions and that Jones gave ’ him blank prescription pads and asked him to forge prescriptions at home. According to Joseph, Jones paid him for the forged prescriptions he produced, which Jones then stored in a box. He testified that the same pattern occurred at the Liotta and Established Pharmacies. Finally, Joseph testified that Muhammad often pressed him to increase both his ordering of narcotics from the wholesalers and his illegal sale and distribution of those drugs at the pharmacies.
Evelyn Dorval, a licensed pharmacist who worked at the Liotta Pharmacy, testified that Jones and Piacente sold controlled substances in the back room. Juanita Solas, who also worked at the Liotta Pharmacy, testified to her own and Jones’ and Piacente’s involvement in the sale of controlled substances. Frederick Ibitoye stated that he had written prescriptions at Liotta Pharmacy at Jones’ and Piacente’s request. Herman Fleming, a clerk and stock-boy at Harlem Pharmacy, asserted that Muhammad and Jones sold drugs illegally there. Fleming also testified that he picked up packages of controlled substances from the Liotta and Brownsville Pharmacies and brought them to the Harlem Pharmacy. Cathy Jo Wilton, administrator of the Greenleaf Clinic and an indicted co-conspirator, testified that she ordered prescription narcotics for the clinic and delivered them to Muhammad at the Harlem Pharmacy. Wilton also testified that she forged prescriptions at Muhammad’s request and that he supplied her with a model prescription form and blank prescription pads.
All of the above witnesses, except the DEA agent and the stockboy at Harlem Pharmacy, testified pursuant to cooperation agreements with the government. At trial these witnesses testified on direct examination regarding the portion of the cooperation agreement that required them to testify truthfully.
Shortly before the district judge charged the jury, defense counsel requested that the alternate jurors not be discharged. One of the regular jurors had indicated that she might have to leave early, and defense counsel indicated that they wanted to facilitate her substitution in that event. Appellants’ counsel urged the trial court to allow two or three alternate jurors to be present during deliberations. Upon being assured that this was the choice of all the appellants, the trial judge granted this re[522] quest. At the end of her charge, Judge Lowe instructed two of the alternate jurors to sit and listen to the jury’s deliberations. She emphasized that although the alternates could be present, they were not to participate.
Less than two hours after the jury had retired, the government’s attorney informed the court that research had revealed that alternates should not be present in a jury room during deliberations. Judge Lowe promptly recalled the jury and discharged the two alternates. At that time the court asked them whether they had participated in the deliberations. One alternate said they had not; the other was ambivalent. The trial judge then instructed the regular jurors to begin their deliberations anew and to disregard all discussions that had been held up to that point. The jury deliberated for another 14 hours before reaching its verdicts.
The district court had directed the jury to return a special verdict on Charles Jones’ continuing criminal enterprise charge, 21 U.S.C. § 848. The jury was requested, among other things, to identify the three predicate narcotics violations necessary to support a § 848 conviction. When the jury returned a guilty verdict on the continuing criminal enterprise charge against Jones, the district court set that verdict aside and entered a judgment of acquittal because it concluded that the jury had improperly relied on § 846 narcotics conspiracy violations as predicate offenses for the § 848 conviction.
Ill
Defendant’s Arguments
A. The Truth-Telling Provisions of the Cooperation Agreements
The defendants complain that by eliciting testimony about the truth-telling portions of the witnesses’ cooperation agreements the government improperly bolstered the witnesses’ credibility and prejudiced defendants. Absent an attack on a witness’ veracity, no evidence is admissible to bolster his credibility. See Fed. R.Evid. 608(a)(2); C. McCormick, Law of Evidence § 49 (2d ed. 1972). Ordinarily the government may not elicit evidence of truth-telling portions of cooperation agreements on direct examination. United States v. Arroyo-Angulo, 580 F.2d 1137, 1146 (2d Cir.), cert. denied, 439 U.S. 913, 1005, 99 S.Ct. 285, 618, 58 L.Ed.2d 260, 681 (1978) and 439 U.S. 1131, 99 S.Ct. 1052, 59 L.Ed.2d 93 (1979). We held in United States v. Maniego, 710 F.2d 24, 27 (2d Cir.1983) (per curiam), that as Fed.R.Evid. 608(a)(2) allows admission of credibility testimony “only after the character of the witness for truthfulness has been attacked by opinion or reputation evidence or otherwise,” such evidence is admissible on direct only if the witness’ credibility was attacked in the opening argument. Here defense counsel attacked the credibility of the government’s witnesses in their opening arguments.
Defense counsel questioned the motives of the government witnesses and commented on their immunity status by stating that it meant they have committed “many crimes, and they are not going to be prosecuted.” Reference was further made in the opening to the fact that one of the government witnesses had previously committed perjury. The jury had to ask itself, another defense counsel said, whether the government witnesses they heard had “made a deal to save their own hide.” Since these opening statements by defense counsel attacked the credibility of the government witnesses, appellants may not be heard to complain at their rehabilitation on direct examination.
B. Presence of Alternate Jurors During Deliberations
Jones and Piaeente assert that the presence of the two alternate jurors in the jury room for about an hour and a half deprived them of a fair trial. Federal Rules of Criminal Procedure 24(c) states: “An alternate juror who does not replace a regular juror shall be discharged after the jury retires to consider its verdict.” Unquestionably, by not discharging the two [523] alternate jurors and allowing them to sit at the beginning of the jury’s deliberations, the district court violated this rule. This mandatory rule is one that trial courts should carefully observe because of the potential for an unfair trial. When alternate jurors are present during deliberations, the possible prejudice is that the defendants are being tried not by a jury of 12, as is their right, but by a larger group. See United States v. Hayutin, 398 F.2d 944, 951 (2d Cir.), cert. denied, 393 U.S. 961, 89 S.Ct. 400, 21 L.Ed.2d 374 (1968); United States v. Allison, 481 F.2d 468, 470 (5th Cir.), aff'd after remand, 487 F.2d 339 (5th Cir.1973), cert. denied, 416 U.S. 982, 94 S.Ct. 2383, 40 L.Ed.2d 759 (1974).
Recently, in United States v. Hillard, 701 F.2d 1052 (2d Cir.), cert. denied, 461 U.S. 958, 103 S.Ct. 2431, 77 L.Ed.2d 1318 (1983), we held that “a violation of Rule 24(c) does not require reversal per se, absent a showing of prejudice.” 701 F.2d at 1058. In Hillard we refused to reverse a conviction when the trial judge substituted an alternate juror for a regular juror who became ill after deliberations had begun. The alternate juror had reaffirmed his ability to consider evidence and to deliberate fully and fairly and indicated that his discussions with the other alternate had not changed in any way his view of the case. Further, the trial judge there instructed the jurors to begin their deliberations over again after the alternate joined them. Because of the district court’s painstaking efforts to minimize potential prejudice to defendants and its determination that there had in fact been no such prejudice, we found that the violation of Rule 24(c) did not constitute reversible error. 701 F.2d at 1061; see also United States v. Mahler, 579 F.2d 730, 737 (2d Cir.), cert. denied, 439 U.S. 872, 991, 99 S.Ct. 205, 592, 58 L.Ed.2d 184, 666 (1978).
Although Hillard was decided on somewhat different facts, its holding that a Rule 24(c) violation does not require reversal absent a showing of prejudice applies here. Hence, in order to determine whether a Rule 24(c) violation mandates a new trial, there must be an analysis of the facts and circumstances at trial. Some factors that should be considered are: (1) whether defendants requested or consented to the alternates’ presence in the jury room; (2) how long the alternates were present; (3) whether the alternates participated in the deliberations; (4) what instruction the trial judge gave before the alternates retired with the regular jurors; (5) what the alternates’ statements subsequently revealed; (6) what curative instructions were given by the trial court to the “reconstituted” jury, i.e., the body without the alternates. An evidentiary hearing should be held where necessary for an evaluation of these factors. See Allison, 481 F.2d at 472.
Here, when the trial court sent the regular jurors out to deliberate and allowed the alternates to accompany them, it specifically instructed the alternates not to participate. The alternates were with the jury for less than two hours. When the alternates were withdrawn and questioned as to whether they had participated and one answered somewhat ambiguously, the trial court called all of the regular jurors before it and instructed that their deliberations must start again from the beginning and they were to disregard any possible participation by the alternates. The jury thereafter deliberated for 14 hours before reaching a verdict. These factors demonstrate the lack of prejudice present in this case. The brief presence of the alternates was at defendants’ request. The trial court instructed the alternates not to participate, but only to sit and listen, and there was a lack of evidence that they had participated. The trial judge gave the reconstituted jury a curative instruction to start its work over again, and the ensuing 14 hours of deliberations before a verdict was reached indicates that whatever possible taint might have crept into the deliberations was effectively removed. Moreover, defendants’ counsel, hoping to avoid a mistrial, argued below that inclusion of the alternates would not be reversible error because defendants had requested that course. The fact that defendants them[524] selves believed that no harm resulted from the alternates’ presence is further proof of a lack of prejudice. Defense counsel requests, which are granted by a trial court, are frequently raised as a claim of error on appeal. We look with disfavor on this trial tactic. United States v. Ferguson, 758 F.2d 843, 851-52 (2d Cir.1985) (conviction affirmed when defendants over government objection expressly requested trial court to charge a lesser crime, one for which defendants had not been indicted); United States v. Young, 745 F.2d 733, 752 (2d Cir.1984) (conviction affirmed despite plain error in jury charge, when that charge was invited by defendant). We hold therefore that the brief presence of alternate jurors during deliberations did not deprive Jones and Piaeente of a fair trial.
IV
Government’s Appeal
Section 848 provides that to have engaged in a continuing criminal enterprise a defendant must have “violate[d] any provision of [Subchapters I or II of Chapter 13 of Title 21],” § 848(b)(1), and such violation must be part of “a continuing series of violations [of Subchapters I or II of Chapter 13 of Title 21],” § 848(b)(2). Further, such violations must be undertaken “in concert with five or more other persons with respect to whom such person occupies a position of organizer, a supervisory position, or any other position of management,” § 848(b)(2)(A). When considering her instructions on defendant Jones’ § 848 continuing criminal enterprise charge, the district judge was concerned that the jury would use as predicate acts either § 846 narcotics conspiracy violations or § 841 substantive narcotics violations that Jones himself did not commit, but of which he was guilty because of his involvement in the conspiracy, see Pinkerton v. United States, 328 U.S. 640, 646-47, 66 S.Ct. 1180, 1183-84, 90 L.Ed. 1489 (1946). The district court believed that because of the § 848(b)(2)(A) “in concert” requirement, conspiracy was a lesser included offense of the continuing criminal enterprise count and, therefore, could not properly be used as one of the § 848(b)(1) predicate acts.
Pinkerton was the only theory of Jones’ liability submitted to the jury on the four substantive counts in the indictment. The only other offense, other than the § 848 continuing criminal enterprise, with which Jones was charged was a § 846 conspiracy. Although there was evidence of substantive narcotics violations by Jones, those violations were not included in the indictment because they occurred outside of the Southern District. The trial court therefore instructed the jury that it could not consider any of the counts in the indictment as predicate violations for a § 848 conviction against Jones. To ensure that it followed her instructions the district judge asked the jury to complete a set of interrogatories. The jury had to list: (a) the three violations of narcotics laws that it found had been proven beyond a reasonable doubt, including “the violation, the pharmacy at which it took place, and the year it took place”; (b) the five persons that it found that Charles Jones organized, supervised or managed; and (c) the names of any pharmacies to be forfeited.
The jury returned verdicts convicting Jones on all six counts of the indictment. In response to Judge Lowe’s first interrogatory on Count Six, the § 848 charge, the jury identified the three predicate violations and the places and times at which they were committed as follows:
1. Jan. 1, 1978-Dec. 31, 1978 Harlem Community Pharmacy Title 21 U.S.Code Sec. 846
2. Jan. 1, 1979-Dec. 31, 1979 Harlem Community Pharmacy Title 21 U.S.Code Sec. 846
3. Jan. 1, 1980-Dec. 31, 1980 Harlem Community Pharmacy Title 21 U.S.Code Sec. 846
Based on these answers, Judge Lowe granted Jones’ request for a judgment of acquittal on the continuing criminal enterprise charge.
In Young, decided after the trial of the instant case, we held that “a lesser includ[525] ed § 846 conspiracy may serve as a predicate offense for a § 848 continuing criminal enterprise.” 745 F.2d at 751-52. We found the statutory language unambiguous: “Section 848(a)(1) provides that any felony violation of Subchapters I and II of Chapter 13 of Title 21 is an eligible predicate.” Id. at 750 (emphasis in original). Similar reasoning applies to a § 841 substantive violation of which defendant is guilty on a Pinkerton theory. This, too, is a violation of a provision of Subchapters I or II of Chapter 13 of Title 21, and as such is an eligible predicate. There is, therefore, no question that the district judge incorrectly instructed the jury not to consider § 846 violations or § 841 violations as predicate violations on a Pinkerton theory.
The fact that the district court made a legal error does not end the matter. The circumstances of the instructions and the verdict on Jones’ § 848 count are far from clear. Whether the government objected to the district court’s incorrect instructions is the first question. Although the government apparently agreed that the § 846 count not be used as a predicate, it did not acquiesce to the court’s charge that substantive § 841 Pinkerton counts could not be predicates.1 Another example of some confusion is the jury’s response on the special verdict form as to which predicate violations it found Jones guilty. The statute that the jury indicated Jones violated was § 846, the narcotics conspiracy law. Yet, the words the jury used tracked exactly the indictment on the § 841 substantive counts for which Jones was found guilty on a Pinkerton theory. The parties agreed, both at the time of trial and on this appeal, that the form of the jury’s answer indicates that it was referring to Jones’ Pinkerton-based § 841 substantive narcotics violations, not the § 846 conspiracy. Understandably, little attempt was made by the district court to resolve this ambiguity since, according to its earlier jury instructions, it believed that neither offense was a proper predicate for a § 848 violation. The dissenting opinion expresses doubts about whether the jury was actually referring to § 841 violations. We see no reason to question a conclusion about which two adverse parties, both of whom were present at trial, have agreed.
In sum, the district court incorrectly instructed the jury that none of the charges in Charles Jones’ indictment could be predicate violations for the § 848 charge. Nonetheless the jury properly using substantive Pinkerton counts as predicate violations, convicted Jones of operating a continuing criminal enterprise. Thus, the fact-finding body found that all of the necessary factual elements of a § 848 violation existed: it found that Jones committed three predicate felony violations; that he acted in concert with five or more persons with respect to whom he occupied a supervisory position; and that he obtained substantial income from these activities. The district judge set aside the verdict not because of a lack of proof of sufficient facts to sustain the conviction, but because of what it incorrectly perceived to be a legal deficiency.
As the only error is one of law, we may correct it if, in so doing, we do not put Jones in jeopardy again for the same offense. So long as there is a jury verdict of guilt, an appellate court may correct errors of law without subjecting a defendant to any constitutional deprivation. See United States v. Zisblatt, 172 F.2d 740, 743 (2d Cir.) (L. Hand, J.), appeal dismissed on the government’s motion, 336 U.S. 934, 69 S.Ct. 750, 93 L.Ed. 1093 (1949). Simply by reinstating the jury’s verdict, we can correct the district court’s legal error. The reinstatement of that verdict does not violate Jones’ double jeopardy rights since he will not be subjected to a second trial for the same offense. When a guilty verdict is reinstated, double jeopardy is not implicated. See United States v. Wilson, 420 U.S. 332, 352-53, 95 S.Ct. 1013, 1026-27, 43 L.Ed.2d 232 (1975).
[526] Accordingly the judgments of conviction are affirmed. The judgment of acquittal for defendant Jones on Count Six, the 21 U.S.C. § 848 charge, is reversed and the jury’s verdict is reinstated. The case is remanded to the district court for resentencing.