I will state a new wall-crossing formula which arose in the study of N=2 supersymmetric field theories coupled to supersymmetric surface defects (joint work with Davide Gaiotto and Greg Moore). This wall-crossing formula is a hybrid between formulas previously written by Cecotti-Vafa and Kontsevich-Soibelman. It should play a role in a yet-undeveloped theory of "open" Donaldson-Thomas invariants. I will briefly explain some examples and applications of the formula.