Does a defendant have a valid challenge to the competency of a prosecution witness at trial?

6 In People v. Burton (1961) 55 Cal.2d 328, 11 Cal.Rptr. 65, 359 P.2d 433, this court observed that the defendant's challenge to the competency of a prosecution witness "could be regarded as impliedly waived by failure to raise it in the trial court," but nonetheless proceeded to consider and reject the claim on the merits because " 'it would be manifestly unfair to affirm appellant's conviction ... merely because of the failure of his attorney to make proper objection in the trial court.' " (At p. 341, 11 Cal.Rptr. 65, 359 P.2d 433, quoting People v. Allen (1955) 131 Cal.App.2d 72, 73, 279 P.2d 996.) We do not read this language as abrogating the requirement that challenges to the competency of a witness be made in the trial court. Rather, it appears that the court was anticipating and responding to a claim of ineffective assistance of trial counsel.