diff --git a/apple1/main.c b/apple1/main.c
index bf422ce..24372fb 100644
--- a/apple1/main.c
+++ b/apple1/main.c
@@ -9,6 +9,7 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <histedit.h>
+#include <signal.h>
 #include <stdlib.h>
 
 #include <dis6502/reverse.h>