diff --git a/test/constexpr_tests.hpp b/test/constexpr_tests.hpp
index a0f638c..3f4acb6 100644
--- a/test/constexpr_tests.hpp
+++ b/test/constexpr_tests.hpp
@@ -15,7 +15,7 @@ namespace boost {
 namespace static_strings {
 
 // char_traits aren't fully constexpr until c++20
-#if BOOST_STATIC_STRING_STANDARD_VERSION <= 201703L && BOOST_STATIC_STRING_STANDARD_VERSION >= 201402L
+#ifdef BOOST_STATIC_STRING_CPP14
 struct cxper_char_traits
 {
   using char_type = char;