That people evaluate themselves more favourably than their average peer on desirable characteristics – the better-than-average effect (BTAE) – is one of the most frequently cited instances of motivated self-enhancement. It has been argued, however, that the BTAE can be rational when the distribution of characteristics is skewed such that most people lie above the mean. We addressed whether the BTAE is present even among people liable to be objectively below average on such characteristics. Prisoners compared their standing on pro-social characteristics – such as kindness, morality, law abidingness – with non-prisoners. Prisoners exhibited the BTAE on every characteristic except law abidingness, for which they viewed themselves as average. Given that prisoners are unlikely to be objectively above average on pro-social characteristics, the findings push for a motivational interpretation of the BTAE.