diff --git a/include/System.h b/include/System.h
index b377b453d1..c64753fe91 100644
--- a/include/System.h
+++ b/include/System.h
@@ -26,6 +26,8 @@
 #include<thread>
 #include<opencv2/core/core.hpp>
 
+#include <unistd.h>
+
 #include "Tracking.h"
 #include "FrameDrawer.h"
 #include "MapDrawer.h"