diff --git a/include/util.h b/include/util.h
index 5d42b780..8e65e6d6 100644
--- a/include/util.h
+++ b/include/util.h
@@ -1,4 +1,9 @@
+#ifndef _SWAY_UTIL_H
+#define _SWAY_UTIL_H
+
 /**
  * Wrap i into the range [0, max[
  */
 int wrap(int i, int max);
+
+#endif
diff --git a/sway/util.c b/sway/util.c
index 25aeb9f4..9a59ddf9 100644
--- a/sway/util.c
+++ b/sway/util.c
@@ -1,3 +1,5 @@
+#include "util.h"
+
 int wrap(int i, int max) {
 	return ((i % max) + max) % max;
 }