diff --git a/asio/include/Makefile.am b/asio/include/Makefile.am
index 474b0f8..fa37daf 100644
--- a/asio/include/Makefile.am
+++ b/asio/include/Makefile.am
@@ -294,6 +294,8 @@
 	asio/execution_context.hpp \
 	asio/executor.hpp \
 	asio/executor_work_guard.hpp \
+	asio/experimental/as_single.hpp \
+	asio/experimental/impl/as_single.hpp \
 	asio/generic/basic_endpoint.hpp \
 	asio/generic/datagram_protocol.hpp \
 	asio/generic/detail/endpoint.hpp \
diff --git a/asio/include/asio/experimental/as_single.hpp b/asio/include/asio/experimental/as_single.hpp
new file mode 100644
index 0000000..5f9b62d
--- /dev/null
+++ b/asio/include/asio/experimental/as_single.hpp
@@ -0,0 +1,124 @@
+//
+// experimental/as_single.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXPERIMENTAL_AS_SINGLE_HPP
+#define ASIO_EXPERIMENTAL_AS_SINGLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/error_code.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+
+/// Completion token type used to specify that an error produced by an
+/// asynchronous operation is captured to an error_code variable.
+/**
+ * The as_single_t class is used to indicate that any error_code produced
+ * by an asynchronous operation is captured to a specified variable.
+ */
+template <typename CompletionToken>
+class as_single_t
+{
+public:
+  /// Default constructor.
+  /**
+   * This constructor is only valid if the underlying completion token is
+   * default constructible.
+   */
+  ASIO_CONSTEXPR as_single_t()
+    : token_()
+  {
+  }
+
+  /// Constructor. 
+  template <typename T>
+  ASIO_CONSTEXPR explicit as_single_t(
+      ASIO_MOVE_ARG(T) completion_token)
+    : token_(ASIO_MOVE_CAST(T)(completion_token))
+  {
+  }
+
+  /// Adapts an executor to add the @c as_single_t completion token as the
+  /// default.
+  template <typename InnerExecutor>
+  struct executor_with_default : InnerExecutor
+  {
+    /// Specify @c as_single_t as the default completion token type.
+    typedef as_single_t default_completion_token_type;
+
+    /// Construct the adapted executor from the inner executor type.
+    executor_with_default(const InnerExecutor& ex) ASIO_NOEXCEPT
+      : InnerExecutor(ex)
+    {
+    }
+
+    /// Convert the specified executor to the inner executor type, then use
+    /// that to construct the adapted executor.
+    template <typename OtherExecutor>
+    executor_with_default(const OtherExecutor& ex,
+        typename enable_if<
+          is_convertible<OtherExecutor, InnerExecutor>::value
+        >::type* = 0) ASIO_NOEXCEPT
+      : InnerExecutor(ex)
+    {
+    }
+  };
+
+  /// Type alias to adapt an I/O object to use @c as_single_t as its
+  /// default completion token type.
+#if defined(ASIO_HAS_ALIAS_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+  template <typename T>
+  using as_default_on_t = typename T::template rebind_executor<
+      executor_with_default<typename T::executor_type> >::other;
+#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+  /// Function helper to adapt an I/O object to use @c as_single_t as its
+  /// default completion token type.
+  template <typename T>
+  static typename decay<T>::type::template rebind_executor<
+      executor_with_default<typename decay<T>::type::executor_type>
+    >::other
+  as_default_on(ASIO_MOVE_ARG(T) object)
+  {
+    return typename decay<T>::type::template rebind_executor<
+        executor_with_default<typename decay<T>::type::executor_type>
+      >::other(ASIO_MOVE_CAST(T)(object));
+  }
+
+//private:
+  CompletionToken token_;
+};
+
+/// Create a completion token to capture error_code values to a variable.
+template <typename CompletionToken>
+inline ASIO_CONSTEXPR as_single_t<typename decay<CompletionToken>::type>
+as_single(ASIO_MOVE_ARG(CompletionToken) completion_token)
+{
+  return as_single_t<typename decay<CompletionToken>::type>(
+      ASIO_MOVE_CAST(CompletionToken)(completion_token));
+}
+
+} // namespace experimental
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/experimental/impl/as_single.hpp"
+
+#endif // ASIO_EXPERIMENTAL_AS_SINGLE_HPP
diff --git a/asio/include/asio/experimental/impl/as_single.hpp b/asio/include/asio/experimental/impl/as_single.hpp
new file mode 100644
index 0000000..fdcc596
--- /dev/null
+++ b/asio/include/asio/experimental/impl/as_single.hpp
@@ -0,0 +1,224 @@
+//
+// experimental/impl/as_single.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_EXPERIMENTAL_AS_SINGLE_HPP
+#define ASIO_IMPL_EXPERIMENTAL_AS_SINGLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#include <tuple>
+
+#include "asio/associated_executor.hpp"
+#include "asio/associated_allocator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_alloc_helpers.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_invoke_helpers.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/variadic_templates.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace experimental {
+namespace detail {
+
+// Class to adapt a as_single_t as a completion handler.
+template <typename Handler>
+class as_single_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename CompletionToken>
+  as_single_handler(as_single_t<CompletionToken> e)
+    : handler_(ASIO_MOVE_CAST(CompletionToken)(e.token_))
+  {
+  }
+
+  template <typename RedirectedHandler>
+  as_single_handler(ASIO_MOVE_ARG(RedirectedHandler) h)
+    : handler_(ASIO_MOVE_CAST(RedirectedHandler)(h))
+  {
+  }
+
+  void operator()()
+  {
+    handler_();
+  }
+
+  template <typename Arg>
+  void operator()(ASIO_MOVE_ARG(Arg) arg)
+  {
+    handler_(ASIO_MOVE_CAST(Arg)(arg));
+  }
+
+  template <typename... Args>
+  void operator()(ASIO_MOVE_ARG(Args)... args)
+  {
+    handler_(std::make_tuple(ASIO_MOVE_CAST(Args)(args)...));
+  }
+
+//private:
+  Handler handler_;
+};
+
+template <typename Handler>
+inline void* asio_handler_allocate(std::size_t size,
+    as_single_handler<Handler>* this_handler)
+{
+  return asio_handler_alloc_helpers::allocate(
+      size, this_handler->handler_);
+}
+
+template <typename Handler>
+inline void asio_handler_deallocate(void* pointer, std::size_t size,
+    as_single_handler<Handler>* this_handler)
+{
+  asio_handler_alloc_helpers::deallocate(
+      pointer, size, this_handler->handler_);
+}
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    as_single_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+}
+
+template <typename Function, typename Handler>
+inline void asio_handler_invoke(Function& function,
+    as_single_handler<Handler>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Function, typename Handler>
+inline void asio_handler_invoke(const Function& function,
+    as_single_handler<Handler>* this_handler)
+{
+  asio_handler_invoke_helpers::invoke(
+      function, this_handler->handler_);
+}
+
+template <typename Signature>
+struct as_single_signature
+{
+  typedef Signature type;
+};
+
+template <typename R>
+struct as_single_signature<R()>
+{
+  typedef R type();
+};
+
+template <typename R, typename Arg>
+struct as_single_signature<R(Arg)>
+{
+  typedef R type(Arg);
+};
+
+template <typename R, typename... Args>
+struct as_single_signature<R(Args...)>
+{
+  typedef R type(std::tuple<typename decay<Args>::type...>);
+};
+
+} // namespace detail
+} // namespace experimental
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Signature>
+struct async_result<experimental::as_single_t<CompletionToken>, Signature>
+{
+  typedef typename async_result<CompletionToken,
+    typename experimental::detail::as_single_signature<Signature>::type>
+      ::return_type return_type;
+
+  template <typename Initiation>
+  struct init_wrapper
+  {
+    init_wrapper(Initiation init)
+      : initiation_(ASIO_MOVE_CAST(Initiation)(init))
+    {
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(
+        ASIO_MOVE_ARG(Handler) handler,
+        ASIO_MOVE_ARG(Args)... args)
+    {
+      ASIO_MOVE_CAST(Initiation)(initiation_)(
+          experimental::detail::as_single_handler<
+            typename decay<Handler>::type>(
+              ASIO_MOVE_CAST(Handler)(handler)),
+          ASIO_MOVE_CAST(Args)(args)...);
+    }
+
+    Initiation initiation_;
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static return_type initiate(
+      ASIO_MOVE_ARG(Initiation) initiation,
+      ASIO_MOVE_ARG(RawCompletionToken) token,
+      ASIO_MOVE_ARG(Args)... args)
+  {
+    return async_initiate<CompletionToken,
+      typename experimental::detail::as_single_signature<Signature>::type>(
+        init_wrapper<typename decay<Initiation>::type>(
+          ASIO_MOVE_CAST(Initiation)(initiation)),
+        token.token_, ASIO_MOVE_CAST(Args)(args)...);
+  }
+};
+
+template <typename Handler, typename Executor>
+struct associated_executor<
+    experimental::detail::as_single_handler<Handler>, Executor>
+{
+  typedef typename associated_executor<Handler, Executor>::type type;
+
+  static type get(
+      const experimental::detail::as_single_handler<Handler>& h,
+      const Executor& ex = Executor()) ASIO_NOEXCEPT
+  {
+    return associated_executor<Handler, Executor>::get(h.handler_, ex);
+  }
+};
+
+template <typename Handler, typename Allocator>
+struct associated_allocator<
+    experimental::detail::as_single_handler<Handler>, Allocator>
+{
+  typedef typename associated_allocator<Handler, Allocator>::type type;
+
+  static type get(
+      const experimental::detail::as_single_handler<Handler>& h,
+      const Allocator& a = Allocator()) ASIO_NOEXCEPT
+  {
+    return associated_allocator<Handler, Allocator>::get(h.handler_, a);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_EXPERIMENTAL_AS_SINGLE_HPP
diff --git a/asio/src/examples/cpp17/Makefile.am b/asio/src/examples/cpp17/Makefile.am
index 4c8195c..f7ce0af 100644
--- a/asio/src/examples/cpp17/Makefile.am
+++ b/asio/src/examples/cpp17/Makefile.am
@@ -14,6 +14,7 @@
 	coroutines_ts/chat_server \
 	coroutines_ts/echo_server \
 	coroutines_ts/echo_server_with_default \
+	coroutines_ts/echo_server_with_as_single_default \
 	coroutines_ts/refactored_echo_server
 endif
 
@@ -23,6 +24,7 @@
 coroutines_ts_chat_server_SOURCES = coroutines_ts/chat_server.cpp
 coroutines_ts_echo_server_SOURCES = coroutines_ts/echo_server.cpp
 coroutines_ts_echo_server_with_default_SOURCES = coroutines_ts/echo_server_with_default.cpp
+coroutines_ts_echo_server_with_as_single_default_SOURCES = coroutines_ts/echo_server_with_as_single_default.cpp
 coroutines_ts_refactored_echo_server_SOURCES = coroutines_ts/refactored_echo_server.cpp
 endif
 
diff --git a/asio/src/examples/cpp17/coroutines_ts/.gitignore b/asio/src/examples/cpp17/coroutines_ts/.gitignore
index 229fd66..ba58f2e 100644
--- a/asio/src/examples/cpp17/coroutines_ts/.gitignore
+++ b/asio/src/examples/cpp17/coroutines_ts/.gitignore
@@ -9,3 +9,4 @@
 *.tds
 *_server
 *_server_with_default
+*_server_with_as_single_default
diff --git a/asio/src/examples/cpp17/coroutines_ts/echo_server_with_as_single_default.cpp b/asio/src/examples/cpp17/coroutines_ts/echo_server_with_as_single_default.cpp
new file mode 100644
index 0000000..457af47
--- /dev/null
+++ b/asio/src/examples/cpp17/coroutines_ts/echo_server_with_as_single_default.cpp
@@ -0,0 +1,71 @@
+//
+// echo_server_with_as_single_default.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <asio/experimental/as_single.hpp>
+#include <asio/co_spawn.hpp>
+#include <asio/detached.hpp>
+#include <asio/io_context.hpp>
+#include <asio/ip/tcp.hpp>
+#include <asio/signal_set.hpp>
+#include <asio/write.hpp>
+#include <cstdio>
+
+using asio::experimental::as_single_t;
+using asio::ip::tcp;
+using asio::awaitable;
+using asio::co_spawn;
+using asio::detached;
+using asio::use_awaitable_t;
+using default_token = as_single_t<use_awaitable_t<>>;
+using tcp_acceptor = default_token::as_default_on_t<tcp::acceptor>;
+using tcp_socket = default_token::as_default_on_t<tcp::socket>;
+namespace this_coro = asio::this_coro;
+
+awaitable<void> echo(tcp_socket socket)
+{
+  char data[1024];
+  for (;;)
+  {
+    auto [e1, nread] = co_await socket.async_read_some(asio::buffer(data));
+    if (nread == 0) break;
+    auto [e2, nwritten] = co_await async_write(socket, asio::buffer(data, nread));
+    if (nwritten != nread) break;
+  }
+}
+
+awaitable<void> listener()
+{
+  auto executor = co_await this_coro::executor;
+  tcp_acceptor acceptor(executor, {tcp::v4(), 55555});
+  for (;;)
+  {
+    if (auto [e, socket] = co_await acceptor.async_accept(); socket.is_open())
+      co_spawn(executor, echo(std::move(socket)), detached);
+  }
+}
+
+int main()
+{
+  try
+  {
+    asio::io_context io_context(1);
+
+    asio::signal_set signals(io_context, SIGINT, SIGTERM);
+    signals.async_wait([&](auto, auto){ io_context.stop(); });
+
+    co_spawn(io_context, listener(), detached);
+
+    io_context.run();
+  }
+  catch (std::exception& e)
+  {
+    std::printf("Exception: %s\n", e.what());
+  }
+}