diff --git a/firmware/include/pentabug/timer.h b/firmware/include/pentabug/timer.h
index 21db3c8..f3f1741 100644
--- a/firmware/include/pentabug/timer.h
+++ b/firmware/include/pentabug/timer.h
@@ -3,6 +3,8 @@
 
 #include <stdint.h>
 
+#include <avr/io.h>
+
 // this library addresses the 16 bit timer
 
 #define PRESCALE_1		(1 << CS10)