diff --git a/jm2cv.cpp b/jm2cv.cpp
index 0902179..1322ee9 100644
--- a/jm2cv.cpp
+++ b/jm2cv.cpp
@@ -2,6 +2,7 @@
 #include <cstring>
 #include <csignal>
 #include <cstdio>
+#include <unistd.h>
 
 #include "cvout.h"
 #include "cvin.h"