diff --git a/src/zmu.cpp b/src/zmu.cpp
index d0476cf6b..e9ec379ac 100644
--- a/src/zmu.cpp
+++ b/src/zmu.cpp
@@ -93,6 +93,7 @@ Options for use with monitors:
 #include "zm_monitor.h"
 #include "zm_local_camera.h"
 #include <getopt.h>
+#include <unistd.h>
 
 void Usage(int status=-1) {
   fputs(