diff --git a/protocol.mk b/protocol.mk
index e057d1d601..d9194b2bfc 100644
--- a/protocol.mk
+++ b/protocol.mk
@@ -15,11 +15,13 @@ endif
 
 ifdef PS2_USE_INT
     SRC += protocol/ps2_interrupt.c
+    SRC += protocol/ps2_io_avr.c
     OPT_DEFS += -DPS2_USE_INT
 endif
 
 ifdef PS2_USE_USART
     SRC += protocol/ps2_usart.c
+    SRC += protocol/ps2_io_avr.c
     OPT_DEFS += -DPS2_USE_USART
 endif
 
diff --git a/protocol/ps2_io_avr.c b/protocol/ps2_io_avr.c
index be13d6696a..ed462345ba 100644
--- a/protocol/ps2_io_avr.c
+++ b/protocol/ps2_io_avr.c
@@ -1,4 +1,5 @@
 #include <stdbool.h>
+#include <avr/io.h>
 #include <util/delay.h>
 
 /* Check port settings for clock and data line */