Improper “vouching” by the government that affects a defendant’s substantial rights will result in reversal. Improper vouching occurs when the prosecutor places the prestige of the government behind a witness by expressing his personal belief that the witness is truthful, or when the prosecutor indicates that information not presented to the jury supports the witness’s testimony. For example, vouching occurs where the witness on direct testimony states that his plea bargain requires him to testify truthfully. Such a statement suggests that the witness who might otherwise be unreliable is compelled by government threats or promises to tell the truth. To determine if vouching is reversible, the reviewing court must balance the seriousness of the vouching against the effectiveness of any curative instruction and the closeness of the case. Here, although there were instances of vouching, because of the curative instructions and the strength of the government’s case, the reviewing court did not find reversible error.