In this paper we extend the probability of error analysis for Viterbi detectors for PAM data transmission to include the effects of steady-state carrier reference errors. It has earlier been found that the Viterbi detector is sensitive to the effects of constant carrier phase errors. However, for two reasonably complicated voiceband pulses taken from the literature, we find that the Viterbi detector is no more sensitive to random carrier phase errors than is a standard quantizing detector.