diff --git a/cmake/platforms/OSX.cmake b/cmake/platforms/OSX.cmake
--- a/cmake/platforms/OSX.cmake
+++ b/cmake/platforms/OSX.cmake
@@ -35,6 +35,8 @@
 string(APPEND CMAKE_C_FLAGS_INIT ${OSX_EXTRA_FLAGS})
 string(APPEND CMAKE_CXX_FLAGS_INIT ${OSX_EXTRA_FLAGS} " -stdlib=libc++")
 
+add_definitions(-DMAC_OSX)
+
 # Ensure we use an OSX specific version of ar, ranlib and nm.
 find_program(CMAKE_AR ${TOOLCHAIN_PREFIX}-ar)
 find_program(CMAKE_RANLIB ${TOOLCHAIN_PREFIX}-ranlib)