Conforming to erroneous memory reports of co-witnesses can have serious impacts on subsequent forensic investigation and court reports. One theoretical explanation proposed is that memory conformity arises due to informational influence; the co-witness desires to give accurate information and reports the co-witness's version because they perceive the co-witness as being more credible. We tested the idea that perceptions of credibility drive memory conformity. We manipulated credibility through expertise; specifically, by telling participants that the (confederate) co-witness had previously worked as either a policeman (high expertise) or an electrician (low expertise). After a discussion with the co-witness, we assessed cued-recall memory and perceptions of credibility about the co-witness and the self. We found that higher expertise led to greater memory conformity. Although higher expertise also led to higher credibility assessments of the co-witness, this was only for perceptions of the credibility as an eye-witness and memory confidence, neither of which predicted memory conformity. By contrast, memory accuracy of the co-witness relative to self-memory accuracy predicted memory conformity, but this was not affected by expertise. These results show support for an informational influence explanation but suggest that expertise perceptions operate differently from our explanation.