People can monitor the accuracy of their own memories and regulate their responses accordingly. But can they monitor and make use of another person's memory? We document a new phenomenon whereby participants neglect a partner's expertise when deciding whether to defer to that partner's memory or to rely on their own. In two experiments, participants studied images for more time than, less time than, or the same amount of time as a partner, and on subsequent recognition tests they were directed to maximize team performance by either answering themselves or letting their partner respond. In both experiments, individuals failed to use the knowledge that the partner would probably have a better memory for certain items. Only when explicitly instructed to estimate their accuracy relative to their partner's did participants take advantage of the partner's greater expertise.