Montez v. State
In Montez v. State, 670 P.2d 694 (Wyo. 1983), the Court held that a defendant who testifies in his own defense during the guilt phase of his trial may be impeached regarding his prior felonies; however, the same information cannot then be used substantively during the habitual offender phase to prove his habitual offender status.
The Court said that doing so would create an impermissible conflict between the defendant's right to testify in his own defense and his right to have the prosecution prove each element of his habitual offender charge beyond a reasonable doubt. Id.