Gerardo Heber Valencia appeals from his conviction for conspiracy to distribute cocaine, 21 U.S.C. § 846 (1982), and distribution of cocaine, 21 U.S.C. § 841(a)(1) (1982). He challenges three rulings by the trial court: (1) admitting testimony that following his arrest, Valencia refused to sign a form waiving his Miranda rights; (2) permitting a DEA agent to testify concerning his interpretation of the word “paperwork” as it was used in a monitored telephone conversation involving Valencia; and (3) delivering its primary charge to the jury, including its instruction concerning the presumption of innocence, prior to the closing arguments by counsel. This court has jurisdiction under 28 U.S.C. § 1291 (1982). We affirm.
FACTUAL BACKGROUND
On September 4, 1983, Joseph Cusanelli, Larry Fuls, and four other men were arrested at the Van Ness Holiday Inn in San Francisco when they attempted to sell 50 kilograms of cocaine to undercover FBI and DEA agents for $2,725,000. After the arrest, Cusanelli identified Valencia as the source of the cocaine. Valencia was arrested later that same day at the Travelodge near San Francisco’s Fisherman’s Wharf.
Cusanelli testified in great detail concerning a series of cocaine transactions in which Valencia, who resides in Florida, allegedly supplied large quantities of cocaine to Cusanelli and Fuls for distribution in their cocaine trafficking operation on the West Coast. The September 4, 1983 attempted sale was the last and by far the largest in this series of transactions. Although Cusanelli’s credibility was challenged because he had entered into a favorable plea agreement with the government, his testimony was fully corroborated by telephone, airline, and hotel records confirming that Valencia had traveled to California and contacted Cusanelli and Fuls at all the critical times when Cusanelli maintained the transactions occurred. It was also supported by the ledger Fuls and Cu-sanelli maintained in their cocaine trafficking business, which reflected all the transactions that Cusanelli claimed had occurred, although it did not contain Valencia’s name.
Moreover, on the day he was arrested, Valencia had on his person Fuls’s current home and business telephone numbers, along with a home telephone number for Fuls that was four months out of date, and three telephone numbers for Cusanelli— two in Florida and one in California. He had placed two separate calls to Fuls and Cusanelli just hours after the sale of the 50 kilograms was scheduled to occur. After the attempted sale occurred and Cusanelli was arrested, Cusanelli made a monitored telephone call to Valencia at the Travel-*1039odge and said to him “[w]e’re done,” and Valencia responded that he wanted to “see ... the paperwork and everything”; Cusa-nelli testified at trial that he and Valencia always used the term “paperwork” in their telephone discussions as a code word to signify money. DEA Special Agent Neal Van Horn also testified at trial, over Valencia’s objection,1 that the term “paperwork” is commonly used by individuals involved in narcotics transactions to refer to money. Valencia’s girlfriend, who was sharing a room with him at the Travelodge, testified that at the time he was arrested, Valencia was waiting to meet Cusanelli because Valencia “was supposed to get some money from him.”
At trial, FBI Special Agent Thomas Car-lon testified that following Valencia’s arrest, Carlon requested Valencia to sign a standard waiver form enumerating his Miranda rights, but Valencia refused. However, according to Carlon, Valencia then made a series of exculpatory statements, commenting that he “wasn’t involved in any cocaine trafficking and ... had merely come to San Francisco to sightsee,” and that he had called his girlfriend in Los Angeles, who joined him in San Francisco. Valencia objected to Carlon’s testimony about the waiver form, contending that it constituted “an impermissible comment on [Valencia’s] assertion of constitutional rights after arrest [and] serv[ed] no relevant purpose whatsoever.” The government maintains that it introduced Carlon’s testimony merely to “lay[] the foundation for the admissibility of [Valencia’s] subsequent statements to Carlon”; the government was seeking to establish that Valencia had been informed of his rights and to “anticipate[ ] an argument by defense counsel [which was never made] that having failed to sign the form[, Valencia] had, in fact, invoked his right to remain silent.” The trial court overruled Valencia’s objection, and admitted Carlon’s testimony.
Following the presentation of all the evidence at Valencia’s trial, but prior to closing arguments by counsel, the trial court delivered its primary charge to the jury concerning the elements of the crimes with which Valencia was charged and the principles of reasonable doubt, the presumption of innocence, and the burden of proof. After the closing arguments, the court did not repeat these instructions in their entirety, but merely explained the mechanics of how the jury should deliberate and arrive at its verdict. Valencia did not object at the time, but now claims that the trial court’s actions violated Federal Rule of Criminal Procedure 302 and constituted “plain error.” He claims that it was prejudicial for “the prosecutor’s closing rebuttal argument ... [to be] the last impression left with the jury” before they began their deliberations, rather than the court’s instructions concerning the applicable law and the presumption of innocence.
ANALYSIS
In his appeal, Valencia challenges the admission of Carlon’s testimony about Valencia’s refusal to sign the Miranda -waiver form, the admission of Van Horn’s testimony about Valencia’s use of the word “paperwork” in his telephone discussion with Cusanelli, and the timing of the trial court’s primary charge to the jury. We agree with Valencia that the trial court erred in permitting Carlon’s testimony concerning Valencia’s refusal to sign the Miranda -waiver form. However, we conclude that in light of the extremely strong and detailed case against Valencia, that error was “harmless beyond a reasonable doubt,” and therefore does not provide a basis for reversal. We find the remaining *1040errors claimed by Valencia to be, at most, harmless, and therefore affirm Valencia’s conviction.
1. Testimony Concerning Valencia’s Refusal To Sign The Waiver Form '
The Supreme Court and this court have consistently held that “it is impermissible to penalize an individual for exercising his fifth amendment privilege [to remain silent] when he is under police custodial interrogation,” and that as a result, prosecutors “may not ... use at trial the fact that [a defendant] stood mute or claimed his privilege in the face of accusation.” Miranda v. Arizona, 384 U.S. 436, 468 n. 37, 86 S.Ct. 1602, 1625 n. 37, 16 L.Ed.2d 694 (1966); accord, United States v. Branson, 756 F.2d 752, 753-54 (9th Cir.1985); Quigg v. Crist, 616 F.2d 1107, 1110 (9th Cir.), cert. denied, 449 U.S. 922, 101 S.Ct. 323, 66 L.Ed.2d 150 (1980); United States v. Wycoff, 545 F.2d 679, 681 (9th Cir.1976), cert. denied, 429 U.S. 1105, 97 S.Ct. 1135, 51 L.Ed.2d 556 (1977); Scarborough v. Arizona, 531 F.2d 959, 961 (9th Cir.1976). “[T]he probative value of [a defendant’s] pretrial silence ... [is generally] outweighed by the prejudicial impact of admitting it into evidence,” United States v. Hale, 422 U.S. 171, 173, 95 S.Ct. 2133, 2135, 45 L.Ed.2d 99 (1975); “every post-arrest silence is insolubly ambiguous,” and therefore is of “little probative force,” yet it carries with it a “strong negative inference” that the defendant is guilty. Doyle v. Ohio, 426 U.S. 610, 617, 96 S.Ct. 2240, 2244, 49 L.Ed.2d 91 (1976); Hale, 422 U.S. at 176, 180, 95 S.Ct. at 2136, 2138. Moreover, it is unfair and misleading for police officers arresting a suspect to inform him of his right to remain silent under Miranda, if there is no “assurance that [his] silence will carry no penalty.” Doyle, 426 U.S. at 617-18, 96 S.Ct. at 2244-45.
Accordingly, it violates due process for a prosecutor to impeach a defendant’s exculpatory story at trial by cross-examining him concerning his silence when he was arrested and received Miranda warnings. Id. at 610, 619, 96 S.Ct. at 2241, 2245. “In a criminal prosecution, it is an error of constitutional proportions to admit evidence that a defendant chose to exercise the right to remain silent after arrest.” Quigg, 616 F.2d at 1110.
We have maintained in a number of cases that “declining to sign a Miranda waiver form [is equivalent to] an assertion of the right to silence____” United States v. Boyce, 594 F.2d 1246, 1250 (9th Cir.), cert. denied, 444 U.S. 855, 100 S.Ct. 112, 62 L.Ed.2d 73 (1979); accord United States v. Heldt, 745 F.2d 1275, 1278 (9th Cir.1984); Wycoff, 545 F.2d at 681.3 A defendant’s refusal to sign a waiver-of-rights form, such as the one Carlon asked Valencia to sign, cannot be introduced into evidence if the defendant remains silent while in custody. See Wycoff, 545 F.2d at 681; United States v. Bridwell, 583 F.2d 1135, 1138-39 (10th Cir.1978) (concluding that admission of testimony on this subject “constituted a clear infringement on defendant’s privilege against self-incrimination”).4 In Wycoff, *1041an agent testified that when he arrested the defendant, advised him of his Miranda rights, and presented him with a waiver form, the defendant “refused to sign” and “said he would rather talk to an attorney” —testimony not unlike Carlon’s in the present case. We noted that
[b]y eliciting such testimony, the government put before the jury the fact that appellant remained silent and requested an attorney. The natural tendency of the use of the testimony in this manner is to prejudice the defendant by attempting to create an inference of guilt in the jury’s mind.
545 F.2d at 681.
In Wycoff, we admonished the government that we were
concerned and alarmed about the increasing attempts by government counsel in this circuit to make reference to or elicit testimony regarding an accused’s silence at the time of arrest. Government counsel are on the verge of the precipice and jeopardizing solid cases by such prac-tice____ In future cases government counsel must scrupulously avoid all reference to or use of an accused’s assertion of his right to remain silent or his right to counsel except where permitted by established rules of law. The conduct here, though we cannot know that it was maliciously deliberate, was reprehensible nevertheless.
545 F.2d at 682; see also Bridwell, 583 F.2d at 1139 (expressing “concern over the seriousness of the error [in admitting testimony concerning the defendant’s refusal to sign a waiver form] at trial”).5
The only exception to the proscription against testimony that defendants have invoked their Miranda rights following arrest is recognized in cases where shortly after invoking their rights, defendants have confessed or made incriminating statements. See United States v. Two Bulls, 577 F.2d 63, 66 (8th Cir.) (per curiam) (testimony concerning defendants’ exercise of their Miranda rights can only be admitted into evidence “[i]n certain atypical situations,” but such a situation is presented when the defendant has made “a later inculpatory statement”), cert. denied, 439 U.S. 931, 99 S.Ct. 322, 58 L.Ed.2d 326 (1978). In such cases, the prosecution must establish that the confession or incriminating statement was made voluntarily before it can be admitted into evidence, and the jury is expected to consider evidence on the issue of voluntariness in determining what weight to give to the confession. See 18 U.S.C. § 3501 (1982).6 *1042Thus, testimony indicating that a defendant fully understood his Miranda rights and freely exercised them prior to making a confession is relevant foundation evidence that the jury should be permitted to consider. Moreover, if a defendant has already confessed or has made other incriminating statements, he will not be significantly prejudiced by testimony that he invoked his Miranda rights prior to making those statements.
Thus, in this limited set of eases, this court and others have permitted testimony that a defendant exercised his Miranda rights. See United States v. Masters, 612 F.2d 1117, 1122 (9th Cir.1979) (permitting testimony that defendant had “express[ed] ... his intention to remain silent during Customs questioning” in order to demonstrate that his subsequent incriminating statements were made voluntarily), cert. denied, 449 U.S. 847, 101 S.Ct. 134, 66 L.Ed.2d 57 (1980); United States v. De La Luz Gallegos, 738 F.2d 378, 383 (10th Cir.) (admitting testimony that defendant requested an attorney prior to making unsolicited, self-incriminating statements to law enforcement officials, because “[t]he knowing exercise of defendant’s right to consult with an attorney before answering questions may refute the inference that any later statement made was involuntary”), cert. denied, — U.S.-, 105 S.Ct. 574, 83 L.Ed.2d 514 (1984); Two Bulls, 577 F.2d at 66 (permitting testimony that after receiving Miranda warnings, defendant who later made inculpatory statements initially refused to give a statement, on grounds that “the knowing exercise of the privilege to remain silent may refute an inference that a later statement was involuntary” and that testimony concerning defendant’s temporary silence constituted “relevant evidence on the issue of voluntariness” under 18 U.S.C. § 3501(a)).
However, when the defendant’s subsequent statements are exculpatory or innocuous, as in Valencia’s case, voluntariness is simply not an issue. In such cases, there is nothing to indicate that the defendant’s statements were involuntarily made, and the defendant does not oppose their admission into evidence. Thus, testimony concerning the defendant’s invocation of Miranda rights is not probative, although it is potentially highly prejudicial.
Unlike cases where the defendant has subsequently made inculpatory statements, in cases like Valencia’s, where the defendant has made only exculpatory or innocuous statements, Miranda -related testimony will be far more prejudicial than the defendant’s subsequent statements: it is the only evidence creating an inference that the defendant is guilty. See Wycoff, 545 F.2d at 681 (testimony about waiver form “ereate[s] an inference of guilt in the jury’s mind”). As a result, the potential prejudicial impact of the Miranda -related testimony will far outweigh any possible probative value such testimony could have. See Hale, 422 U.S. at 173, 95 S.Ct. at 2135 (probative value of defendant’s exercise of Miranda rights is outweighed by the prejudicial impact of admitting it into evidence). We therefore hold that the. admission of such testimony violates due process. The district court erred in admitting agent Car-Ion’s testimony that Valencia refused to sign the Miranda -waiver form.7
*1043 2. Valencia’s Remaining Claims
Valencia’s two remaining claims are largely without merit. The testimony by agent Van Horn concerning the meaning of the word “paperwork” during Valencia’s monitored conversation with Cusanelli was merely cumulative: Cusanelli had previously testified that the two men always used the term to signify money in their telephone conversations. As a result, Van Horn’s testimony provided, at most, indirect corroboration for Cusanelli’s testimony. Moreover, in his cross-examination of agent Van Horn, Valencia’s attorney skillfully extracted a series of concessions from Van Horn that Cusanelli and Valencia could have been referring to a variety of items when they used the word “paperwork,” including financial documents; Valencia’s counsel also had ample opportunity to dispute Van Horn’s prof erred interpretation in his closing argument. See United States v. Smith, 519 F.2d 516, 521 (9th Cir.1975); United States v. McCoy, 539 F.2d 1050, 1062 (5th Cir.1976), cert. denied, 431 U.S. 919, 97 S.Ct. 2185, 53 L.Ed.2d 230 (1977). Thus, even if there was not sufficient foundation for agent Van Horn to testify as an expert or lay witness concerning the terminology customarily employed in cocaine transactions, see United States v. Fleishman, 684 F.2d 1329, 1335-36 (9th Cir.), cert. denied, 459 U.S. 1044, 103 S.Ct. 464, 74 L.Ed.2d 614 (1982); see also United States v. Rogers, 769 F.2d 1418, 1425 (9th Cir.1985), we conclude that his testimony concerning the term “paperwork” did not prejudice Valencia’s defense.
Valencia’s claim that the timing of the trial court’s primary charge to the jury violated Federal Rule 30 is also without merit. This court has held that a trial court’s violation of Rule 30 constitutes reversible error only if it results in actual prejudice to the defendant. See United States v. McCown, 711 F.2d 1441, 1452 (9th Cir.1983); United States v. Abushi, 682 F.2d 1289, 1303 (9th Cir.1982); United States v. Harvill, 501 F.2d 295, 296-97 (9th Cir.1974). In the present case, Valencia does not contend that the trial court’s instructions were “misleading or inadequate” in any way, United States v. Pazsint, 703 F.2d 420, 424 (9th Cir.1983), or that they omitted any essential information; his challenge is based exclusively upon the time at which they were given. Valencia does not contend that his counsel’s argument would have been any different had it been delivered prior to the trial court’s primary charge to the jury. Moreover, in its final instructions to the jury, following the parties’ closing arguments, the trial court reiterated the principle that the burden was on the government to prove its case beyond a reasonable doubt. As a result, even though the timing of the district court’s primary charge did not comply with Rule 30,8 we cannot conclude that this resulted in actual prejudice to Valencia.9
3. Harmless-Error Analysis
Although the district court erred in permitting agent Carlon to testify concerning Valencia’s refusal to sign the Miranda-waiver form, and although such an error will in many cases require reversal of a conviction, in light of the powerful oral testimony and documentary evidence linking Valencia to the Fuls-Cusanelli cocaine conspiracy, we conclude that the error in this case was “harmless beyond a reasonable doubt.” See Chapman v. California, 386 U.S. 18, 24, 87 S.Ct. 824, 828, 17 L.Ed.2d 705 (1967); Wycoff 545 F.2d at *1044682; Bridwell, 583 F.2d at 1139. Moreover, even were we to assume that the district court also erred in admitting agent Van Horn’s testimony concerning the use of the term “paperwork” in the telephone conversation between Valencia and Cusa-nelli, our conclusion would be the same.
AFFIRMED.