From f90ce170d56241fc0049a697bb27fe981960a50f Mon Sep 17 00:00:00 2001
From: Christopher Kohlhoff <chris@kohlhoff.com>
Date: Sun, 17 Oct 2021 11:10:23 +1100
Subject: [PATCH] Fix multi-signature handling when variadic templates are
 disabled.

---
 include/boost/asio/async_result.hpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/boost/asio/async_result.hpp b/include/boost/asio/async_result.hpp
index e4a8d31d..d1a95ab1 100644
--- a/include/boost/asio/async_result.hpp
+++ b/include/boost/asio/async_result.hpp
@@ -312,6 +312,12 @@ struct are_simple_completion_signatures<Sig0, Sig1, Sig2>
 {
 };
 
+template <>
+struct simple_completion_signature<void>
+{
+  typedef void type;
+};
+
 template <typename R>
 struct simple_completion_signature<R()>
 {