diff --git a/src/libmodbus/modbus.c b/src/libmodbus/modbus.c
index af3b240..f7eeddd 100644
--- a/src/libmodbus/modbus.c
+++ b/src/libmodbus/modbus.c
@@ -19,6 +19,7 @@
 #include <unistd.h>
 #endif
 #ifdef ARDUINO
+#include <Arduino.h>
 
 #ifndef DEBUG
 #define printf(...) {}