diff --git a/ModFile.cc b/ModFile.cc
index e19ff0af05a93468edaa5ac15b57e581c5c46736..e36c43f2f329af690e539da24410ab9610f6303d 100644
--- a/ModFile.cc
+++ b/ModFile.cc
@@ -22,6 +22,10 @@
 #include <fstream>
 #include <typeinfo>
 #include <cassert>
+#ifndef _WIN32
+# include <unistd.h>
+#endif
+
 #include "ModFile.hh"
 #include "ConfigFile.hh"
 #include "ComputingTasks.hh"