I will explain how Joyce's wall-crossing formulae for invariants counting semistable objects in an abelian category A may be understood as Stokes phenomena for a connection on the Riemann sphere taking value in the Ringel-Hall Lie algebra of A. This allows one in particular to interpret his holomorphic generating functions as defining an isomonodromic family of such connections parametrised by the space of stability conditions of A. This is joint work with T. Bridgeland (arXiv:0801.3974).