diff --git a/include/signal.h b/include/signal.h
index ed70c4f177..f33aef2c71 100644
--- a/include/signal.h
+++ b/include/signal.h
@@ -46,8 +46,9 @@
 
 /* All signals are "real time" signals */
 
-#define SIGRTMIN        MIN_SIGNO  /* First real time signal */
-#define SIGRTMAX        MAX_SIGNO  /* Last real time signal */
+#define SIGRTMIN        MIN_SIGNO       /* First real time signal */
+#define SIGRTMAX        MAX_SIGNO       /* Last real time signal */
+#define _NSIG           (MAX_SIGNO + 1) /* Biggest signal number + 1 */
 
 /* NuttX does not support all standard signal actions.  NuttX supports what
  * are referred to as "real time" signals.  The default action of all NuttX