--- a/src/external/luajit/CMakeLists-LUAJIT.txt
+++ b/src/external/luajit/CMakeLists-LUAJIT.txt
@@ -22,6 +22,9 @@ endif()
 # CPU detection
 if(${CMAKE_HOST_SYSTEM_PROCESSOR} STREQUAL x86_64)
   add_definitions(-DLUAJIT_TARGET=LUAJIT_ARCH_X64)
+# hack because on OSX CMAKE_HOST_SYSTEM_PROCESSOR is always i386
+elseif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+  add_definitions(-DLUAJIT_TARGET=LUAJIT_ARCH_X64)
 elseif (${CMAKE_HOST_SYSTEM_PROCESSOR} STREQUAL i386)
   add_definitions(-DLUAJIT_TARGET=LUAJIT_ARCH_x86)
 elseif(${CMAKE_HOST_SYSTEM_PROCESSOR} STREQUAL x86)