In order to understand how electoral rules affect political outcomes, we need to know whether and how voters react to them. The ability of voters to react strategically to electoral rules may be limited in cases where the electoral rules are complex. In this article, I look for evidence of rational reactions to a moderately complex electoral system, that used in the Federal Republic of Germany. By examining district-level election results, I find substantial evidence that voters do react rationally, despite the complexity of the two-vote system. The rational reactions by voters lead to excess first votes for incumbents, for candidates of the major party expected to be in government, to major-party candidates in close races and to major-party candidates in districts with significant minority-party support. The findings support both the general claim that voters can react strategically to complex electoral rules, and more specific claims about the value of the two-vote ballot in Germany.