Public participation is widely considered to be an indispensable part of contemporary constitution-making processes, largely because it is thought to create a sense of public ownership of the new constitution. However, as recent research has shown that public participation has little actual impact on the content of the constitution, this supposed link is puzzling. How can ineffective participation contribute to public support for the constitution? We address this puzzle by subjecting it to experimental tests. In two recontact survey experiments conducted across six countries, we empirically tested the effects of various forms of participation at the constitution drafting stage and their concrete impact on public support for the constitution. We found that the act of participating in itself has little effect on support for the constitution but that broader cues that give the impressions of a fair process can have significant positive effects. This indicates that participation in constitution drafting can increase public support for a constitution regardless of the extent to which it has an impact on the constitutional text and that the appearance of a fair process is the link between participation and support.