diff --git a/src/tools.c b/src/tools.c
index 2043693..14d8aaf 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -24,6 +24,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include <string.h>
 #include "shape.h"
 #include "boxes.h"