Empirical literature has primarily studied the effects of electoral systems on ‘ballot box’ turnout: the number of votes cast divided by the number of eligible voters. However, changes in the share of blank and null votes associated with variation in electoral rules are often as large as electoral system effects on ‘ballot box’ turnout. I present evidence in this sense by re-analysing existing regression discontinuity (RD) studies that leverage population-based threshold in local electoral rules, showing that substantive inferences on the relationship between electoral rules and participation may be substantively overturned, depending on whether we consider ‘ballot box’ or ‘valid’ turnout. I theorise that blank voting can be conceptualised as ‘voluntary’ non-voting, due to voters not finding suitable options on the ballot paper, whereas null voting expresses ‘involuntary’ non-voting, due to voters filling out their ballot incorrectly. Leveraging local election returns from Italy (1960-1970) and Poland (2010-2024), I leverage population-based discontinuities in electoral rules, as well as exogenous electoral system reforms (in 1964 and 2011 respectively) to test the implications of this framework. I find that the occurrence of blank voting is significantly lower when electoral rules increase the number of parties that enter electoral competition, while ballot complexity increases the occurrence of null voting. In both case studies, it emerges that the effects of electoral rules on ‘voluntary’ non-voting are more pronounced in high-education locales, while the effects of electoral rules ‘involuntary’ non-voting are stronger in low-education locales. I conclude by discussing normative implications for designing inclusive electoral rules.