Contemporary Western legal systems allow any individual to serve as a witness and to testify in court. However, in legal regimes from late antiquity we find strict limitations on the eligibility of certain types of people to serve as witnesses. Some of the lists of disqualified witnesses are very particular, thus inviting explanation of the reasons for the specific rules of disqualification. Such is the case regarding both Jewish and Roman rules of disqualification, which are the topic of this paper. Tannaitic halakha, composed in Roman Palestine between the first and third centuries CE, includes a list of four characters disqualified from giving testimony, which has long defied interpretation: “a dice player, a usurer, pigeon flyers, and traders in Seventh Year produce”. This paper offers a novel approach to the study of this list, suggesting that the rabbis drew on the Roman legal institution of infamia when constructing their own laws regarding disqualified witnesses. Beyond solving a puzzle relating to Jewish law, the paper also sheds light on the inner logic of Roman law, maintaining that Jewish and Roman rules of disqualified witnesses are commonly grounded in an ethics of self-control. By drawing attention to this previously unnoted theoretical subtext, the paper contributes to a missing chapter in the global history of evidence admissibility rules.