diff --git a/NN/volume.c b/NN/volume.c
index d83ab6bcdb9269e05b49cbedc0556b15cc08b508..08c8250ddd751dd436bd02398b30a10378140038 100644
--- a/NN/volume.c
+++ b/NN/volume.c
@@ -1,6 +1,7 @@
 #include <stdlib.h>
 #include <ctype.h>
 #include <math.h>
+#include <stdio.h>
 /*--------------------------------------------------------------
 
     This file contains six recursive C routines for calculating