diff --git a/src/mu-cmd-index.c b/src/mu-cmd-index.c
index b5536bb2..a7d05007 100644
--- a/src/mu-cmd-index.c
+++ b/src/mu-cmd-index.c
@@ -22,6 +22,7 @@
 #include <errno.h>
 #include <string.h>
 #include <stdio.h>
+#include <signal.h>
 
 #include "mu-util.h"
 #include "mu-util-xapian.h"