diff --git a/lib/libwebsockets.h b/lib/libwebsockets.h
index 16f294fd..2fd78b18 100644
--- a/lib/libwebsockets.h
+++ b/lib/libwebsockets.h
@@ -65,7 +65,9 @@ typedef SSIZE_T ssize_t;
 #else // NOT WIN32
 
 /* to get ppoll() */
-#define __USE_GNU
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
 #include <poll.h>
 #include <unistd.h>