--- src/config.h
+++ src/config.h
@@ -31,6 +31,7 @@
 #define __CONFIG_H

 #ifdef __APPLE__
+#define _DARWIN_C_SOURCE
 #include <fcntl.h> // for fcntl(fd, F_FULLFSYNC)
 #include <AvailabilityMacros.h>
 #endif