We show that quantitative easing (QE) worsens government debt sustainability. In our model, the government runs a primary deficit with elastic debt demand that makes interest rates endogenous. The central bank has long-term capital and remits profits to the fiscal authority. QE depletes this capital stock, reducing future remittances and crisis-fighting reserves. Contrary to Sargent and Wallace (1981), where greater monetary accommodation lowers the steadystate debt level, we show that QE increases the steady-state level of debt and shifts the default boundary inward, thus heightening fragility and reducing debt sustainability. Moreover, while QE can keep interest rates low for extended periods, continued debt accumulation eventually triggers a sharp rise in financing costs. Under certain parameters, large-scale QE makes previously sustainable debt levels unsustainable, leading ultimately to sovereign default.