Collateral attacks on previous proceedings are impermissible unless the attack is grounded upon the court's lack of jurisdiction over the parties or subject matter. State v. Smith, 269 Neb. 773, 696 N.W.2d 871 (2005). Only a void judgment is subject to collateral attack. Mayfield v. Hartmann, 221 Neb. 122, 375 N.W.2d 146 (1985). Although Keen's 1998 DUI conviction may have been voidable and subject to reversal upon appeal, it was not void.
We conclude that Keen's 1998 DUI conviction was valid for the purpose of sentence enhancement and that Keen is attempting to collaterally attack that conviction. Therefore, we affirm the judgment of the district court on this issue.