diff --git a/cores/arduino/wiring.h b/cores/arduino/wiring.h
index 6f61293..0118618 100755
--- a/cores/arduino/wiring.h
+++ b/cores/arduino/wiring.h
@@ -26,6 +26,7 @@
 #define Wiring_h
 
 #include <avr/io.h>
+#include <stdlib.h>
 #include "binary.h"
 
 #ifdef __cplusplus