diff --git a/src/DDS.h b/src/DDS.h
index ef6d193..8d408eb 100644
--- a/src/DDS.h
+++ b/src/DDS.h
@@ -1,6 +1,7 @@
 #ifndef _DDS_H_
 #define _DDS_H_
 
+#include <Arduino.h>
 #include <avr/pgmspace.h>
 
 // Use pin 3 for PWM? If not defined, use pin 11