In general, the public budget can be financed by taxes or public debt. Governments have an incentive to finance the public budget with public debt if current generations do not consider the consequences of debt financing for future generations when making their decisions. In order to limit the negative consequences for future generations, many democratic countries have introduced fiscal rules, such as the debt ceiling in the United States, the Maastricht 3%-Deficit-Criterion for EU member states or the German debt brake. Quite often, these rules have the disadvantage that they prevent the financing of cost-intensive, welfare-increasing long-term projects, e.g. in connection with the climate change or in the event of an economic or political crisis. In this paper, we discuss a new form of fiscal rule, namely a flexible majority rule on public debt spending. With the flexible majority rule, the majority required to increase public debt depends on the amount of the increase itself. We show that under specific circumstances the flexible majority rule can increase social welfare especially within a crisis in which the willingness to finance public spending with debt is higher than in normal times.