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Starting from the observation of taxpayers’ heterogeneity in terms of honesty and of the existence of a perverse social dynamic leading the most honest to evade, we propose a simple mechanism to restore honesty. In a laboratory experiment, we test the willingness of subjects to voluntarily contribute to a fund dedicated to finance the fight against tax evasion. This voluntary contribution mechanism, without redistribution, is analyzed thanks to several treatments that differ depending on the type and the level of the required contribution. We show: 1) that a substantial number of subjects contribute and that the frequency of contribution decreases with the increase in the level of contribution; 2) that the most honest taxpayers are those who contribute; and 3) that risk aversion deters subjects to contribute, while inequality aversion encourages them. Finally, in line with the literature on tax evasion, we confirm that the increase in the audit probability, which is observed only in groups where the collective contribution is sufficient, reduces evasion in these groups. Classification JEL : H26, C91, C72, D03, D6.