diff --git a/Source/kwsys/SystemTools.cxx b/Source/kwsys/SystemTools.cxx
index 7c26974ef8..f610a7050b 100644
--- a/Source/kwsys/SystemTools.cxx
+++ b/Source/kwsys/SystemTools.cxx
@@ -14,6 +14,10 @@
 #  endif
 #endif
 
+#if defined(_WIN32) && !defined(_WIN32_WINNT)
+#  define _WIN32_WINNT _WIN32_WINNT_VISTA
+#endif
+
 #include "kwsysPrivate.h"
 #include KWSYS_HEADER(RegularExpression.hxx)
 #include KWSYS_HEADER(SystemTools.hxx)