diff --git a/CMakeLists.txt b/CMakeLists.txt
index c502b4d..4b78dbe 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,6 +42,8 @@ if ("${CMAKE_SYSTEM_NAME}" MATCHES "BSD")
 	# Need this for SIGWINCH in FreeBSD and OpenBSD respectively;
 	# our POSIX version macros make it undefined
 	add_definitions (-D__BSD_VISIBLE=1 -D_BSD_SOURCE=1)
+elseif (APPLE)
+	add_definitions (-D_DARWIN_C_SOURCE)
 endif ()
 
 set (project_libraries ${LibEV_LIBRARIES} ${Termo_LIBRARIES}