diff --git a/tmate-slave.c b/tmate-slave.c
index 273a45f5..470d81dd 100644
--- a/tmate-slave.c
+++ b/tmate-slave.c
@@ -18,6 +18,7 @@
 #include <fcntl.h>
 #include <sys/syslog.h>
 #include <sched.h>
+#include <signal.h>
 #include "tmate.h"
 
 struct tmate_session _tmate_session, *tmate_session = &_tmate_session;