diff --git a/utilities.cpp b/utilities.cpp
index cd093dd..8770480 100644
--- a/utilities.cpp
+++ b/utilities.cpp
@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <strings.h>
+#include <unistd.h>
 #include <memory>
 
 #include "ioparport.h"