diff --git a/vm/master.hpp b/vm/master.hpp
index 6409d65494..6164c9ea30 100755
--- a/vm/master.hpp
+++ b/vm/master.hpp
@@ -19,6 +19,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+#include <unistd.h>
 #include <sys/param.h>
 
 /* C++ headers */