Witnesses frequently make an error when reporting events they have observed. Although some error in witness reports is to be expected and does not mean the testimony as a whole is flawed, an important question is how such an error affects judgments of credibility of the witness. In 2 experiments we investigated the impact of a single demonstrated (probative or nonprobative) detail inaccuracy on judgments of the likely reliability of witness memory. Potential mediators (witness dishonesty and forgetfulness) were examined to explain the relationship between inaccuracy and perceived reliability of the witness’s memory report. The presence of a single inaccuracy affected observers’ judgments of the reliability of the other elements of testimony and the testimony as a whole. There was also some evidence that the less probative the detail the more other elements of the reported account of the event were questioned. The mediation analyses showed that a single testimonial error contributed to the witness being perceived as dishonest or forgetful, attributions that in turn shaped perceptions of witness credibility. These findings suggest that legal professionals should be cautious when highlighting an isolated testimonial error given the potential for it to suggest more widespread testimonial unreliability.