diff --git a/targets/libraries/Wire/utility/twi.c b/targets/libraries/Wire/utility/twi.c
index bb49a92f9..dc90b21f9 100644
--- a/targets/libraries/Wire/utility/twi.c
+++ b/targets/libraries/Wire/utility/twi.c
@@ -22,6 +22,7 @@
 #include <inttypes.h>
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include <avr/signal.h>
 #include <compat/twi.h>
 
 #ifndef cbi