Hidden public liabilities are a pervasive but poorly measured feature of sovereign balance sheets. When they are eventually revealed, they can reprice sovereign risk overnight and compress the policy space between painful fiscal adjustment and default. This paper studies optimal sovereign default following the revelation of hidden debt. We develop a quantitative model of optimal sovereign default following a hidden-debt revelation and apply it to Senegal's 2024 shock, in which an incoming administration uncovered more than ten billion dollars in off-balance-sheet obligations, revising central-government debt upward by 50 percentage points of GDP. […]