Research on mixed electoral systems provides inconclusive findings on the question whether members of parliament (MPs) elected in single-member districts are more likely to vote against the party line than MPs elected via closed party lists. This article rejects both the hypothesis of a general “mandate divide” and the competing claim that contamination effects completely wash out behavioral differences. Instead, we argue that electoral incentives to defect are stronger for a specific type of MP—those who run only in a district and are electorally insecure. Statistical analyses of roll call votes in the German Bundestag covering more than 60 years support this “conditional mandate divide” against alternative hypotheses. These findings suggest a more nuanced view on electoral system effects in mixed electoral systems and highlight the importance of electoral competition for incentivizing MPs to side with district demands if those conflict with the party line.