--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp1y/udlit-char-template2.C	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,23 @@
+// PR c++/85864
+// { dg-do compile { target c++14 } }
+
+template<class T, T... S> struct String_template {};
+
+template<class C, C... S>
+constexpr String_template<C, S...> operator""_template() {
+    return String_template<C, S...> {};
+}
+
+template<class prefix = decltype("0x"_template), class T>
+int hex(T v) { return 1; }
+
+template<int v> 
+void tt2() {
+  //    auto h2 = hex<decltype("0x"_template)>(1);
+    auto h = hex(2);
+}
+
+int main() {
+  //    auto h = hex(2);
+  //    return h;
+}