Index: include/tuple
===================================================================
--- include/tuple
+++ include/tuple
@@ -1012,10 +1012,21 @@
 
 template <class _T1, class ..._Args>
 struct __find_exactly_one_checked {
-  static constexpr bool __matches[] = {is_same<_T1, _Args>::value...};
+#if defined(__clang__) && __clang_major__ > 5 && __cplusplus > 201402L
+    // Workaround https://bugs.llvm.org/show_bug.cgi?id=28385
+    inline _LIBCPP_INLINE_VISIBILITY
+    static constexpr size_t __index()
+    {
+        constexpr bool __matches[] = {is_same<_T1, _Args>::value...};
+        return __find_detail::__find_idx(0, __matches);
+    }
+    static constexpr size_t value = __index();
+#else
+    static constexpr bool __matches[] = {is_same<_T1, _Args>::value...};
     static constexpr size_t value = __find_detail::__find_idx(0, __matches);
-    static_assert (value != __not_found, "type not found in type list" );
-    static_assert(value != __ambiguous,"type occurs more than once in type list");
+#endif
+    static_assert(value != __not_found, "type not found in type list" );
+    static_assert(value != __ambiguous, "type occurs more than once in type list");
 };
 
 template <class _T1>