diff --git a/include/boost/config/compiler/clang.hpp b/include/boost/config/compiler/clang.hpp
index a1463a0d..3ba62096 100644
--- a/include/boost/config/compiler/clang.hpp
+++ b/include/boost/config/compiler/clang.hpp
@@ -39,7 +39,7 @@
 #  define BOOST_NO_TYPEID
 #endif
 
-#if !__is_identifier(__int64) && !defined(__GNUC__)
+#if defined(__is_identifier) && !__is_identifier(__int64) && !defined(__GNUC__)
 #  define BOOST_HAS_MS_INT64
 #endif