diff --git a/CMakeLists.txt b/CMakeLists.txt
index 26fe76c..d1b2ddc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -56,6 +56,10 @@
   add_definitions(-DOS_WINDOWS)
 endif()
 
+if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
+  add_definitions(-DOS_FREEBSD)
+endif()
+
 # Set CPU
 if(${CMAKE_SYSTEM_PROCESSOR} MATCHES "x86")
   add_definitions(-DARCH_X86)