Armstrong and the modal inversion of dispositions

D.M. Armstrong has objected that the dispositionalist theory of laws and properties is modally inverted, for it entails that properties are constituted by relations to non-actual possibilia. I contend that if this objection succeeds against dispositionalism, then Armstrong's nomic necessitation relation is also modally inverted. This shows that at least one of Armstrong's reasons for preferring a nomic necessitation theory is specious.