This article reports on an Internet-based quasi-experiment that took place during the French 2012 presidential election. We designed a website where French voters could vote under different voting rules. Based on the observation of more than 8,000 participants, we find that a substantial minority (10% to 15%) vote differently under the different systems, with 17% of the voters not voting for their preferred candidate in the one-round election, this percentage dropped to 12% in the alternative vote (first choice). Compared to the two-rounds election, at the aggregate level, the top two candidates get slightly more votes under one round, while the minor candidates obtain more first choices under the alternative vote. These findings are consistent with what the literature suggests about the impact of these voting systems on voters' choice.