diff --git a/core/vul/vul_temp_filename.cxx b/core/vul/vul_temp_filename.cxx
index 4921a04..731fee0 100644
--- a/core/vul/vul_temp_filename.cxx
+++ b/core/vul/vul_temp_filename.cxx
@@ -11,7 +11,7 @@
 
 #if defined(_MSC_VER) || defined(__MINGW32__)
 
-#  include <Windows.h>
+#  include <windows.h>
 #else
 #  if defined(unix) || defined(__unix) || defined(__unix__) || defined(__APPLE__)
 // Helper functions for Unix