High electoral turnout in countries with compulsory voting systems is often attributed to citizens' desire to avoid the legal consequences for abstention. However, turnout is equally high in compulsory voting contexts where penalties are absent or unenforced, which challenges this notion. An alternative perspective suggests that citizens’ lack of knowledge about the absence of penalties or their enforcement drives turnout, but little is known about the causal effect of such knowledge. This study examines whether knowledge of compulsory voting rules and their (lack of) enforcement influences turnout likelihood. To do so, we focus on Belgium, a country with a long history of compulsory voting – including high levels of turnout – but without enforcement of the legal consequences for abstention. We conduct a vignette survey experiment to analyse how factual information about compulsory voting, potential penalties for abstention, and the absence of enforcement of these penalties influences citizens’ likelihood of voting in future elections. By examining how knowledge of compulsory voting rules influences electoral participation, this research deepens our understanding of the effects of such rules on turnout in democratic systems.