Setting aside all exclusion-style worries about the redundancy of postulating additional, non-physical mental causes for effects that can already be explained in purely physical terms, dualists who treat mental properties as supervening on physical properties still face a further problem: in cases of mental-to-mental causation, they cannot avoid positing an implausibly coincidental coordination in the timing of the distinct causal processes terminating, respectively, in the mental effect and its physical base. I argue that this problem arises regardless of whether one treats the mental cause as causing both the mental effect and its physical base, or whether one treats the latter as having instead been caused by some physical state, and that the problem also does not depend on which theory of causation one adopts. A third option of treating the mental cause and its physical base as producing the mental effect and its physical base by a single causal process that they both contribute to is found to come up short as well.