diff --git a/src/sleep.cc b/src/sleep.cc
index 918abc48..1449339e 100644
--- a/src/sleep.cc
+++ b/src/sleep.cc
@@ -15,6 +15,7 @@
 #include "sleep.h"
 
 #include <cerrno>
+#include <cstdlib>
 #include <ctime>
 
 #include "internal_macros.h"