diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 1456f547..a8587dad 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -687,7 +687,6 @@ if(CMAKE_COMPILER_IS_GNUCC)
 	set(CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_WITHDEBINFO} -O2")
 	set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${WARN_LDFLAGS}")
 	set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${WARN_LDFLAGS}")
-	add_definitions(-D_GNU_SOURCE)
 endif()
 
 if((NOT APPLE) OR CMAKE_COMPILER_IS_GNUCC)
diff --git a/src/config.h.cmake b/src/config.h.cmake
index 8b1f4636..bd3da228 100644
--- a/src/config.h.cmake
+++ b/src/config.h.cmake
@@ -8,6 +8,10 @@
 #define PACKAGE_VERSION "${PACKAGE_VERSION}"
 #define LIBRARY_DIR "${LIGHTTPD_LIBRARY_DIR}"
 
+#ifndef _GNU_SOURCE
+# define _GNU_SOURCE
+#endif
+
 /* System */
 #cmakedefine  HAVE_SYS_DEVPOLL_H
 #cmakedefine  HAVE_SYS_EPOLL_H