Do changes in local electoral institutions impact national-level elections? This paper argues that mass parties uniquely benefit from introducing party-centered electoral institutions at the local level. To test this hypothesis, I take advantage of a local governance reform in early 20th century Sweden, where the local governance type was decided by a population threshold. I find that municipalities that used a traditional type of local governance, community meetings, had higher support for the conservatives in national elections. In contrast, municipalities that used elections and representatives for local governance had higher national-level support for the communists and social democrats. A crucial difference between these parties is the way that they are organized: the social democrats and communists are organized as mass parties that rely on local branches and members as their main electoral strategy. The conservatives, on the other hand, are a typical elite party that is more dependent on connections to the bureaucracy and media than on local branches and members. These findings highlight how spillovers between different levels of politics matter for scholars, who want to evaluate the policy consequences of institutional reforms.