Can't build for OSX or Linux

I’ve been working on a game in Unity for a long time. I’ve made numerous builds to Windows, OSX, Linux, and Web Player. However, with the most recent version, I am unable to make a Linux or OSX build. When I open the build settings, only Windows appears in the target platforms under standalone. Also, when I try to build using my custom build script, I get this error: Building a player for ‘Mac’ (2) target is not supported in this Unity build.

Did you include the Mac and Linux modules when installing Unity? With 5.3 they split the modules out so you can choose only certain ones you need, defaults to only Windows selected I believe.