diff --git a/libraries/USBHost/src/printhex.h b/libraries/USBHost/src/printhex.h
index 98c1ae6023855e1da36aebd26cf5d5eff5bead1e..60dcd064fcc8163d7442773c8997eaef844b185a 100644
--- a/libraries/USBHost/src/printhex.h
+++ b/libraries/USBHost/src/printhex.h
@@ -20,6 +20,8 @@ e-mail   :  support@circuitsathome.com
 #else
 #define __PRINTHEX_H__
 
+#include <Arduino.h>
+
 void E_Notifyc(char c, int lvl);
 
 template <class T>