--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/lookup/pr87531.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,73 @@
+// PR c+/87531 lookup of operator= in templates
+// { dg-do run }
+
+struct Base {
+  void operator= (Base const&);
+};
+
+void Base::operator= (Base const &)
+{
+}
+
+template <typename T>
+struct Derived : Base
+{
+  T v;
+
+  Derived() : v (0) {}
+  Derived(T v_) : v (v_) {}
+
+  T &assign1 (Derived const& rhs)
+  {
+    operator=(rhs); // erroneously bound to Base::operator=
+    return v;
+  }
+
+  T &assign2 (Derived const& rhs)
+  {
+    this->operator=(rhs); // erroneously bound to Base::operator=
+    return v;
+  }
+};
+
+template <typename T>
+struct Single
+{
+  T v;
+
+  Single () : v (0) {}
+  Single (T v_) : v (v_) {}
+
+  T &assign1 (Single const& rhs)
+  {
+    operator=(rhs); // lookup failed
+    return v;
+  }
+
+  T &assign2 (Single const& rhs)
+  {
+    this->operator=(rhs); // Marked as dependent, happened to work
+    return v;
+  }
+};
+
+int main()
+{
+  Derived<int> a, b(123);
+
+  if (a.assign1 (b) != 123)
+    return 1;
+
+  if (a.assign2 (b) != 123)
+    return 2;
+
+  Single<int> c, d(123);
+  
+  if (c.assign1 (d) != 123)
+    return 3;
+
+  if (c.assign2 (d) != 123)
+    return 4;
+
+  return 0;
+}