diff --git a/wmtop/wmtop.c b/wmtop/wmtop.c
index a1409de..3585a0d 100644
--- a/wmtop/wmtop.c
+++ b/wmtop/wmtop.c
@@ -27,6 +27,8 @@
 #error No operating system selected
 #endif /* !defined(OS_DEFINED) */
 
+#define _BSD_SOURCE
+
 /******************************************/
 /* Includes                               */
 /******************************************/