Why do countries set sovereign debt ceilings if they keep raising them? This paper shows that debt ceilings can serve as intermediate commitment devices that reduce expected dilution, thereby lowering spreads—and their volatility—even without reducing total borrowing. We propose a new sovereign default model with long-term debt in which each government inherits a previously announced ceiling but may revise it by paying a political or institutional deviation cost. This friction generates a state-dependent form of partial commitment. The ceiling mitigates debt dilution at the expense of fiscal flexibility, leading the government to voluntarily adopt a ceiling that limits the discretion of its future selves. Governments choose rules that are costly—but not impossible—to adjust, trading off lower spreads and volatility through reduced dilution against the option value of fiscal flexibility in bad times. Consistent with this mechanism, we show that emerging-market countries operating under fiscal rules exhibit lower sovereign spreads and lower spread volatility, even though breaches and revisions occur.