We investigate the implications of fiscal fatigue � governments� declining ability to increase primary fiscal balances with rising public debt - utilising the cubic policy rule estimated by Ghosh et al. (2013). We characterize its equilibrium debt-output ratios and fiscal space, and analyze its dynamic stability in the deterministic (long-run) case. There may be up to three equilibria, of which the intermediate one will typically require a stability criterion stricter than fiscal solvency. We illustrate numerically for six developed economies.