We study a dynamic setting in which a firm chooses its debt maturity structure and default timing endogenously, both without commitment. The firm, who is waiting for the arrival of an upside event, commits to keep its outstanding bond face-values constant, but controls its debt maturity structure via the fraction of newly issued short-term bonds when refinancing its maturing long- and short-term bonds. As a baseline, we show that when the firm’s fundamental is time-invariant, it is impossible to have a shortening equilibrium in which the firm keeps issuing short-term bonds and consequently defaults inefficiently. However, when cash-flows deteriorate over time so that the debt recovery value is affected by the endogenous default timing, then a shortening equilibrium with accelerated default can emerge. In this situation, self-enforcing shortening and lengthening equilibria exist, and the shortening equilibrium may be Pareto-dominated by the lengthening one.