iPhone + OSX targets on the same project

I created a project with two targets, one for iPhone and another for Mac OsX. They both build and run well when I build them the first time (I built the OsX target first then iPhone target next). However, if I build the iPhone target and switch back to OsX target, the OsX target now thinks that it uses the iPhone SDK rather than it's own mac OsX SDK, and doesn't compile anymore (can't find the OSX SDK header files). I created a project with two targets, one for i