diff --git a/fmacros.h b/fmacros.h
index 7635180..24c9bac 100644
--- a/fmacros.h
+++ b/fmacros.h
@@ -12,10 +12,8 @@
 
 #if defined(__sun__)
 #define _POSIX_C_SOURCE 200112L
-#elif defined(__linux__) || defined(__OpenBSD__) || defined(__NetBSD__)
-#define _XOPEN_SOURCE 600
 #else
-#define _XOPEN_SOURCE
+#define _XOPEN_SOURCE 600
 #endif
 
 #if defined(__APPLE__) && defined(__MACH__)