--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/coroutines/co-return-syntax-08-bad-return.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,43 @@
+//  { dg-additional-options "-fsyntax-only -w" }
+
+#include "coro.h"
+
+struct Coro {
+  struct promise_type;
+  using handle_type = coro::coroutine_handle<Coro::promise_type>;
+  handle_type handle;
+  Coro () : handle(0) {}
+  Coro (handle_type _handle) : handle(_handle) {}
+  Coro (Coro &&s) : handle(s.handle) { s.handle = nullptr; }
+  Coro &operator = (Coro &&s) {
+	handle = s.handle;
+	s.handle = nullptr;
+	return *this;
+  }
+  Coro (const Coro &) = delete;
+  ~Coro() {
+    if ( handle )
+      handle.destroy();
+  }
+  struct promise_type {
+  promise_type() {}
+  ~promise_type() {}
+  Coro get_return_object () { return Coro (handle_type::from_promise (*this)); }
+  auto initial_suspend () { return coro::suspend_always{}; }
+  auto final_suspend () { return coro::suspend_always{}; }
+  void return_void () { }
+   void unhandled_exception() { }
+  };
+};
+
+extern int x;
+
+// Diagnose disallowed "return" in coroutine.
+Coro
+bar () // { dg-error {a 'return' statement is not allowed} }
+{
+  if (x)
+    return Coro(); 
+  else
+    co_return;
+}