diff --git a/tool/MasterDevice.cpp b/tool/MasterDevice.cpp
index e88551c1..fffd6b38 100644
--- a/tool/MasterDevice.cpp
+++ b/tool/MasterDevice.cpp
@@ -9,6 +9,7 @@
 #include <errno.h>
 #include <sys/ioctl.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <sstream>
 #include <iomanip>