diff --git a/include/internal/catch_external_interfaces.h b/include/internal/catch_external_interfaces.h
index 7243ed7b..dffd5187 100644
--- a/include/internal/catch_external_interfaces.h
+++ b/include/internal/catch_external_interfaces.h
@@ -4,10 +4,10 @@
  *  Distributed under the Boost Software License, Version 1.0. (See accompanying
  *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  */
-#ifndef TWOBLUECUBES_CATCH_EXTERNAL_INTERFACES_H
-#define TWOBLUECUBES_CATCH_EXTERNAL_INTERFACES_H
+#ifndef TWOBLUECUBES_CATCH_EXTERNAL_INTERFACES_H_INCLUDED
+#define TWOBLUECUBES_CATCH_EXTERNAL_INTERFACES_H_INCLUDED
 
 #include "../reporters/catch_reporter_bases.hpp"
 #include "catch_reporter_registrars.hpp"
 
-#endif // TWOBLUECUBES_CATCH_EXTERNAL_INTERFACES_H
+#endif // TWOBLUECUBES_CATCH_EXTERNAL_INTERFACES_H_INCLUDED