-# It used to break on FreeBSD within Boost headers and was only activated in maintainer mode, but I hope it works nowadays
-set(warnCFLAGS "${warnCFLAGS} -Wundef")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wundef")
+if("${CMAKE_SYSTEM}" MATCHES "Linux") # Breaks on FreeBSD within Boost headers :(
+ set(warnCFLAGS "${warnCFLAGS} -Wundef")
+ set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wundef")
+endif()