Background and objectives: Overconfidence in errors is a well-replicated cognitive bias in psychosis. However, prior studies have sometimes failed to find differences between patients and controls for more difficult tasks. We pursued the hypothesis that overconfidence in errors is exaggerated in participants with a liability to psychosis relative to controls only when they feel competent in the respective topic and/or deem the question easy. Whereas subjective competence likely enhances confidence in those with low psychosis liability as well, we still expected to find more 'residual' caution in the latter group. Methods: We adopted a psychometric high-risk approach to circumvent the confounding influence of treatment. A total of 2321 individuals from the general population were administered a task modeled after the "Who wants to be a millionaire" quiz. Participants were requested to endorse one out of four response options, graded for confidence, and were asked to provide ratings regarding subjective competence for the knowledge domain as well as the subjective difficulty of each item. Results: In line with our assumption, overconfidence in errors was increased overall in participants scoring high on the Paranoia Checklist core paranoia subscale (2 SD above the mean). This pattern of results was particularly prominent for items for which participants considered themselves competent and which they rated as easy. Limitations: Results need to be replicated in a clinical sample. Discussion: In support of our hypothesis, subjective competence and task difficulty moderate overconfidence in errors in psychosis. Trainings that teach patients the fallibility of human cognition may help reduce delusional ideation. (C) 2015 Published by Elsevier Ltd.