--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr88395.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,23 @@
+// { dg-do compile { target c++2a } }
+
+template <class T, class U>
+concept Concept2 = requires (T t, U u)
+{
+    t += u; // { dg-error "template instantiation depth" }
+};
+
+template <class T>
+concept Concept = Concept2 <T, T>;
+
+struct S
+{
+    template <Concept T>
+    constexpr S& operator += (T o);
+};
+
+constexpr S operator * (S a, S b)
+{
+    return a += b;
+}
+
+// { dg-prune-output "compilation terminated" }