1 files changed, 13 insertions, 0 deletions
diff --git a/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/length.pass.cpp b/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/length.pass.cpp
index ff5a2a934a9f..5d882bde2f5a 100644
--- a/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/length.pass.cpp
+++ b/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char16_t/length.pass.cpp
@@ -12,12 +12,21 @@
 // template<> struct char_traits<char16_t>
 
 // static size_t length(const char_type* s);
+// constexpr in C++17
 
 #include <string>
 #include <cassert>
 
 #include "test_macros.h"
 
+#if TEST_STD_VER > 14
+constexpr bool test_constexpr()
+{
+    return std::char_traits<char16_t>::length(u"") == 0
+        && std::char_traits<char16_t>::length(u"abcd") == 4;
+}
+#endif
+
 int main()
 {
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
@@ -28,5 +37,9 @@ int main()
     assert(std::char_traits<char16_t>::length(u"aaa") == 3);
     assert(std::char_traits<char16_t>::length(u"aaaa") == 4);
 #endif
+
+#if TEST_STD_VER > 14
+    static_assert(test_constexpr(), "" );
+#endif
 #endif  // _LIBCPP_HAS_NO_UNICODE_CHARS
 }