Individual differences in prosocial behaviour are well-documented. Increasingly, there has been a focus on the specific situations in which particular personality traits predict prosocial behaviour. HEXACO Honesty-Humility—the basic trait most consistently linked to prosocial behaviour in prior studies—has been found to predict prosociality most strongly in situations that afford the exploitation of others. Importantly, though, it may be the subjectively perceived situation that affords the behavioural expression of a trait. Following this reasoning, we tested the proposition that Honesty-Humility would predict prosocial behaviour more strongly in situations characterised by, and perceived to contain, two dimensions of interdependence that can afford exploitation: high conflict and high power. However, across a series of incentivised economic games and two large experience sampling studies, we only found inconsistent evidence for the association between Honesty-Humility and prosocial behaviour. Furthermore, the link between Honesty-Humility and prosociality was neither conditional on objective interdependence nor on subjective perceptions of interdependence. Nonetheless, perceptions of conflict and power tracked objective properties of economic games and were related to prosocial behaviour in the lab and field. Future research should take individuals' subjective understanding of situations into account, which may also help understand the (generalisability of the) effect of Honesty-Humility on prosocial behaviour.