diff --git a/lib/zebra.h b/lib/zebra.h
index 7d907ed..3a93b7a 100644
--- a/lib/zebra.h
+++ b/lib/zebra.h
@@ -25,6 +25,10 @@
 #include "config.h"
 #endif /* HAVE_CONFIG_H */
 
+#ifdef GNU_LINUX
+#define _GNU_SOURCE
+#endif /* GNU_LINUX */
+
 #ifdef SUNOS_5
 #define _XPG4_2
 #define __EXTENSIONS__