diff --git a/asio_compatibility.hpp b/asio_compatibility.hpp
new file mode 100644
index 0000000..8b6c7ed
--- /dev/null
+++ b/asio_compatibility.hpp
@@ -0,0 +1,69 @@
+#ifndef SIMPLE_WEB_ASIO_HPP
+#define SIMPLE_WEB_ASIO_HPP
+
+#include <memory>
+
+#ifdef USE_STANDALONE_ASIO
+#include <asio.hpp>
+#include <asio/steady_timer.hpp>
+namespace SimpleWeb {
+  using error_code = std::error_code;
+  using errc = std::errc;
+  using system_error = std::system_error;
+  namespace make_error_code = std;
+} // namespace SimpleWeb
+#else
+#include <boost/asio.hpp>
+#include <boost/asio/steady_timer.hpp>
+namespace SimpleWeb {
+  namespace asio = boost::asio;
+  using error_code = boost::system::error_code;
+  namespace errc = boost::system::errc;
+  using system_error = boost::system::system_error;
+  namespace make_error_code = boost::system::errc;
+} // namespace SimpleWeb
+#endif
+
+namespace SimpleWeb {
+#if(USE_STANDALONE_ASIO && ASIO_VERSION >= 101300) || BOOST_ASIO_VERSION >= 101300
+  using io_context = asio::io_context;
+  using resolver_results = asio::ip::tcp::resolver::results_type;
+  using async_connect_endpoint = asio::ip::tcp::endpoint;
+
+  inline void restart(io_context &context) noexcept {
+    context.restart();
+  }
+  inline asio::ip::address make_address(const std::string &str) noexcept {
+    return asio::ip::make_address(str);
+  }
+  template <typename socket_type>
+  asio::executor get_socket_executor(socket_type &socket) {
+    return socket.get_executor();
+  }
+  template <typename handler_type>
+  void async_resolve(asio::ip::tcp::resolver &resolver, const std::pair<std::string, std::string> &host_port, handler_type &&handler) {
+    resolver.async_resolve(host_port.first, host_port.second, std::forward<handler_type>(handler));
+  }
+#else
+  using io_context = asio::io_service;
+  using resolver_results = asio::ip::tcp::resolver::iterator;
+  using async_connect_endpoint = asio::ip::tcp::resolver::iterator;
+
+  inline void restart(io_context &context) noexcept {
+    context.reset();
+  }
+  inline asio::ip::address make_address(const std::string &str) noexcept {
+    return asio::ip::address::from_string(str);
+  }
+  template <typename socket_type>
+  io_context &get_socket_executor(socket_type &socket) {
+    return socket.get_io_service();
+  }
+  template <typename handler_type>
+  void async_resolve(asio::ip::tcp::resolver &resolver, const std::pair<std::string, std::string> &host_port, handler_type &&handler) {
+    resolver.async_resolve(asio::ip::tcp::resolver::query(host_port.first, host_port.second), std::forward<handler_type>(handler));
+  }
+#endif
+} // namespace SimpleWeb
+
+#endif /* SIMPLE_WEB_ASIO_HPP */
diff --git a/client_http.hpp b/client_http.hpp
index 4c8b085..5d1a1d0 100644
--- a/client_http.hpp
+++ b/client_http.hpp
@@ -1,6 +1,7 @@
 #ifndef CLIENT_HTTP_HPP
 #define CLIENT_HTTP_HPP
 
+#include "asio_compatibility.hpp"
 #include "utility.hpp"
 #include <limits>
 #include <mutex>
@@ -8,27 +9,6 @@
 #include <unordered_set>
 #include <vector>
 
-#ifdef USE_STANDALONE_ASIO
-#include <asio.hpp>
-#include <asio/steady_timer.hpp>
-namespace SimpleWeb {
-  using error_code = std::error_code;
-  using errc = std::errc;
-  using system_error = std::system_error;
-  namespace make_error_code = std;
-} // namespace SimpleWeb
-#else
-#include <boost/asio.hpp>
-#include <boost/asio/steady_timer.hpp>
-namespace SimpleWeb {
-  namespace asio = boost::asio;
-  using error_code = boost::system::error_code;
-  namespace errc = boost::system::errc;
-  using system_error = boost::system::system_error;
-  namespace make_error_code = boost::system::errc;
-} // namespace SimpleWeb
-#endif
-
 namespace SimpleWeb {
   template <class socket_type>
   class Client;
@@ -119,21 +99,25 @@ namespace SimpleWeb {
           timer = nullptr;
           return;
         }
-        timer = std::unique_ptr<asio::steady_timer>(new asio::steady_timer(socket->get_io_service()));
-        timer->expires_from_now(std::chrono::seconds(seconds));
-        auto self = this->shared_from_this();
-        timer->async_wait([self](const error_code &ec) {
+        timer = std::unique_ptr<asio::steady_timer>(new asio::steady_timer(get_socket_executor(*socket), std::chrono::seconds(seconds)));
+        std::weak_ptr<Connection> self_weak(this->shared_from_this()); // To avoid keeping Connection instance alive longer than needed
+        timer->async_wait([self_weak](const error_code &ec) {
           if(!ec) {
-            error_code ec;
-            self->socket->lowest_layer().cancel(ec);
+            if(auto self = self_weak.lock()) {
+              error_code ec;
+              self->socket->lowest_layer().cancel(ec);
+            }
           }
         });
       }
 
       void cancel_timeout() noexcept {
         if(timer) {
-          error_code ec;
-          timer->cancel(ec);
+          try {
+            timer->cancel();
+          }
+          catch(...) {
+          }
         }
       }
     };
@@ -155,7 +139,7 @@ namespace SimpleWeb {
 
     /// If you have your own asio::io_service, store its pointer here before calling request().
     /// When using asynchronous requests, running the io_service is up to the programmer.
-    std::shared_ptr<asio::io_service> io_service;
+    std::shared_ptr<io_context> io_service;
 
     /// Convenience function to perform synchronous request. The io_service is run within this function.
     /// If reusing the io_service for other tasks, use the asynchronous request functions instead.
@@ -178,7 +162,7 @@ namespace SimpleWeb {
         std::lock_guard<std::mutex> lock(concurrent_synchronous_requests_mutex);
         --concurrent_synchronous_requests;
         if(!concurrent_synchronous_requests)
-          io_service->reset();
+          restart(*io_service);
       }
 
       if(ec)
@@ -208,7 +192,7 @@ namespace SimpleWeb {
         std::lock_guard<std::mutex> lock(concurrent_synchronous_requests_mutex);
         --concurrent_synchronous_requests;
         if(!concurrent_synchronous_requests)
-          io_service->reset();
+          restart(*io_service);
       }
 
       if(ec)
@@ -362,7 +346,7 @@ namespace SimpleWeb {
     unsigned short port;
     unsigned short default_port;
 
-    std::unique_ptr<asio::ip::tcp::resolver::query> query;
+    std::unique_ptr<std::pair<std::string, std::string>> host_port;
 
     std::unordered_set<std::shared_ptr<Connection>> connections;
     std::mutex connections_mutex;
@@ -383,7 +367,7 @@ namespace SimpleWeb {
       std::lock_guard<std::mutex> lock(connections_mutex);
 
       if(!io_service) {
-        io_service = std::make_shared<asio::io_service>();
+        io_service = std::make_shared<io_context>();
         internal_io_service = true;
       }
 
@@ -400,12 +384,12 @@ namespace SimpleWeb {
       connection->attempt_reconnect = true;
       connection->in_use = true;
 
-      if(!query) {
+      if(!host_port) {
         if(config.proxy_server.empty())
-          query = std::unique_ptr<asio::ip::tcp::resolver::query>(new asio::ip::tcp::resolver::query(host, std::to_string(port)));
+          host_port = std::unique_ptr<std::pair<std::string, std::string>>(new std::pair<std::string, std::string>(host, std::to_string(port)));
         else {
           auto proxy_host_port = parse_host_port(config.proxy_server, 8080);
-          query = std::unique_ptr<asio::ip::tcp::resolver::query>(new asio::ip::tcp::resolver::query(proxy_host_port.first, std::to_string(proxy_host_port.second)));
+          host_port = std::unique_ptr<std::pair<std::string, std::string>>(new std::pair<std::string, std::string>(proxy_host_port.first, std::to_string(proxy_host_port.second)));
         }
       }
 
@@ -656,14 +640,14 @@ namespace SimpleWeb {
       if(!session->connection->socket->lowest_layer().is_open()) {
         auto resolver = std::make_shared<asio::ip::tcp::resolver>(*io_service);
         session->connection->set_timeout(config.timeout_connect);
-        resolver->async_resolve(*query, [this, session, resolver](const error_code &ec, asio::ip::tcp::resolver::iterator it) {
+        async_resolve(*resolver, *host_port, [this, session, resolver](const error_code &ec, resolver_results results) {
           session->connection->cancel_timeout();
           auto lock = session->connection->handler_runner->continue_lock();
           if(!lock)
             return;
           if(!ec) {
             session->connection->set_timeout(config.timeout_connect);
-            asio::async_connect(*session->connection->socket, it, [this, session, resolver](const error_code &ec, asio::ip::tcp::resolver::iterator /*it*/) {
+            asio::async_connect(*session->connection->socket, results, [this, session, resolver](const error_code &ec, async_connect_endpoint /*endpoint*/) {
               session->connection->cancel_timeout();
               auto lock = session->connection->handler_runner->continue_lock();
               if(!lock)
diff --git a/client_https.hpp b/client_https.hpp
index a5f9f7c..09eecf5 100644
--- a/client_https.hpp
+++ b/client_https.hpp
@@ -47,13 +47,13 @@ namespace SimpleWeb {
     void connect(const std::shared_ptr<Session> &session) override {
       if(!session->connection->socket->lowest_layer().is_open()) {
         auto resolver = std::make_shared<asio::ip::tcp::resolver>(*io_service);
-        resolver->async_resolve(*query, [this, session, resolver](const error_code &ec, asio::ip::tcp::resolver::iterator it) {
+        async_resolve(*resolver, *host_port, [this, session, resolver](const error_code &ec, resolver_results results) {
           auto lock = session->connection->handler_runner->continue_lock();
           if(!lock)
             return;
           if(!ec) {
             session->connection->set_timeout(this->config.timeout_connect);
-            asio::async_connect(session->connection->socket->lowest_layer(), it, [this, session, resolver](const error_code &ec, asio::ip::tcp::resolver::iterator /*it*/) {
+            asio::async_connect(session->connection->socket->lowest_layer(), results, [this, session, resolver](const error_code &ec, async_connect_endpoint /*endpoint*/) {
               session->connection->cancel_timeout();
               auto lock = session->connection->handler_runner->continue_lock();
               if(!lock)
diff --git a/server_http.hpp b/server_http.hpp
index 59ec711..2321964 100644
--- a/server_http.hpp
+++ b/server_http.hpp
@@ -1,6 +1,7 @@
 #ifndef SERVER_HTTP_HPP
 #define SERVER_HTTP_HPP
 
+#include "asio_compatibility.hpp"
 #include "utility.hpp"
 #include <functional>
 #include <iostream>
@@ -12,25 +13,6 @@
 #include <thread>
 #include <unordered_set>
 
-#ifdef USE_STANDALONE_ASIO
-#include <asio.hpp>
-#include <asio/steady_timer.hpp>
-namespace SimpleWeb {
-  using error_code = std::error_code;
-  using errc = std::errc;
-  namespace make_error_code = std;
-} // namespace SimpleWeb
-#else
-#include <boost/asio.hpp>
-#include <boost/asio/steady_timer.hpp>
-namespace SimpleWeb {
-  namespace asio = boost::asio;
-  using error_code = boost::system::error_code;
-  namespace errc = boost::system::errc;
-  namespace make_error_code = boost::system::errc;
-} // namespace SimpleWeb
-#endif
-
 // Late 2017 TODO: remove the following checks and always use std::regex
 #ifdef USE_BOOST_REGEX
 #include <boost/regex.hpp>
@@ -63,10 +45,10 @@ namespace SimpleWeb {
       std::shared_ptr<Session> session;
       long timeout_content;
 
-      asio::io_service::strand strand;
+      std::mutex send_queue_mutex;
       std::list<std::pair<std::shared_ptr<asio::streambuf>, std::function<void(const error_code &)>>> send_queue;
 
-      Response(std::shared_ptr<Session> session_, long timeout_content) noexcept : std::ostream(nullptr), session(std::move(session_)), timeout_content(timeout_content), strand(session->connection->socket->get_io_service()) {
+      Response(std::shared_ptr<Session> session_, long timeout_content) noexcept : std::ostream(nullptr), session(std::move(session_)), timeout_content(timeout_content) {
         rdbuf(streambuf.get());
       }
 
@@ -88,30 +70,40 @@ namespace SimpleWeb {
           *this << "\r\n";
       }
 
+      /// send_queue_mutex must be locked here
       void send_from_queue() {
         auto self = this->shared_from_this();
-        strand.post([self]() {
-          asio::async_write(*self->session->connection->socket, *self->send_queue.begin()->first, self->strand.wrap([self](const error_code &ec, std::size_t /*bytes_transferred*/) {
-            auto lock = self->session->connection->handler_runner->continue_lock();
-            if(!lock)
-              return;
+        asio::async_write(*self->session->connection->socket, *send_queue.begin()->first, [self](const error_code &ec, std::size_t /*bytes_transferred*/) {
+          auto lock = self->session->connection->handler_runner->continue_lock();
+          if(!lock)
+            return;
+          {
+            std::unique_lock<std::mutex> lock(self->send_queue_mutex);
             if(!ec) {
               auto it = self->send_queue.begin();
-              if(it->second)
-                it->second(ec);
+              auto callback = std::move(it->second);
               self->send_queue.erase(it);
               if(self->send_queue.size() > 0)
                 self->send_from_queue();
+
+              lock.unlock();
+              if(callback)
+                callback(ec);
             }
             else {
               // All handlers in the queue is called with ec:
+              std::vector<std::function<void(const error_code &)>> callbacks;
               for(auto &pair : self->send_queue) {
                 if(pair.second)
-                  pair.second(ec);
+                  callbacks.emplace_back(std::move(pair.second));
               }
               self->send_queue.clear();
+
+              lock.unlock();
+              for(auto &callback : callbacks)
+                callback(ec);
             }
-          }));
+          }
         });
       }
 
@@ -141,12 +133,10 @@ namespace SimpleWeb {
         this->streambuf = std::unique_ptr<asio::streambuf>(new asio::streambuf());
         rdbuf(this->streambuf.get());
 
-        auto self = this->shared_from_this();
-        strand.post([self, streambuf, callback]() {
-          self->send_queue.emplace_back(streambuf, callback);
-          if(self->send_queue.size() == 1)
-            self->send_from_queue();
-        });
+        std::lock_guard<std::mutex> lock(send_queue_mutex);
+        send_queue.emplace_back(streambuf, callback);
+        if(send_queue.size() == 1)
+          send_from_queue();
       }
 
       /// Write directly to stream buffer using std::ostream::write
@@ -296,19 +286,23 @@ namespace SimpleWeb {
           return;
         }
 
-        timer = std::unique_ptr<asio::steady_timer>(new asio::steady_timer(socket->get_io_service()));
-        timer->expires_from_now(std::chrono::seconds(seconds));
-        auto self = this->shared_from_this();
-        timer->async_wait([self](const error_code &ec) {
-          if(!ec)
-            self->close();
+        timer = std::unique_ptr<asio::steady_timer>(new asio::steady_timer(get_socket_executor(*socket), std::chrono::seconds(seconds)));
+        std::weak_ptr<Connection> self_weak(this->shared_from_this()); // To avoid keeping Connection instance alive longer than needed
+        timer->async_wait([self_weak](const error_code &ec) {
+          if(!ec) {
+            if(auto self = self_weak.lock())
+              self->close();
+          }
         });
       }
 
       void cancel_timeout() noexcept {
         if(timer) {
-          error_code ec;
-          timer->cancel(ec);
+          try {
+            timer->cancel();
+          }
+          catch(...) {
+          }
         }
       }
     };
@@ -380,7 +374,7 @@ namespace SimpleWeb {
     std::function<void(std::unique_ptr<socket_type> &, std::shared_ptr<typename ServerBase<socket_type>::Request>)> on_upgrade;
 
     /// If you have your own asio::io_service, store its pointer here before running start().
-    std::shared_ptr<asio::io_service> io_service;
+    std::shared_ptr<io_context> io_service;
 
     /// If you know the server port in advance, use start() instead.
     /// Returns assigned port. If io_service is not set, an internal io_service is created instead.
@@ -388,12 +382,12 @@ namespace SimpleWeb {
     unsigned short bind() {
       asio::ip::tcp::endpoint endpoint;
       if(config.address.size() > 0)
-        endpoint = asio::ip::tcp::endpoint(asio::ip::address::from_string(config.address), config.port);
+        endpoint = asio::ip::tcp::endpoint(make_address(config.address), config.port);
       else
         endpoint = asio::ip::tcp::endpoint(asio::ip::tcp::v6(), config.port);
 
       if(!io_service) {
-        io_service = std::make_shared<asio::io_service>();
+        io_service = std::make_shared<io_context>();
         internal_io_service = true;
       }
 
@@ -424,7 +418,7 @@ namespace SimpleWeb {
 
       if(internal_io_service) {
         if(io_service->stopped())
-          io_service->reset();
+          restart(*io_service);
 
         // If thread_pool_size>1, start m_io_service.run() in (thread_pool_size-1) threads for thread-pooling
         threads.clear();
diff --git a/tests/io_test.cpp b/tests/io_test.cpp
index d15270b..ebed11c 100644
--- a/tests/io_test.cpp
+++ b/tests/io_test.cpp
@@ -4,10 +4,6 @@
 
 using namespace std;
 
-#ifndef USE_STANDALONE_ASIO
-namespace asio = boost::asio;
-#endif
-
 using HttpServer = SimpleWeb::Server<SimpleWeb::HTTP>;
 using HttpClient = SimpleWeb::Client<SimpleWeb::HTTP>;
 
@@ -315,12 +311,33 @@ int main() {
       for(auto &thread : threads)
         thread.join();
       ASSERT(client.connections.size() == 100);
-      client.io_service->reset();
+      SimpleWeb::restart(*client.io_service);
       client.io_service->run();
       ASSERT(client.connections.size() == 1);
       for(auto call : calls)
         ASSERT(call);
     }
+
+    // Test concurrent requests from different clients
+    {
+      vector<int> calls(10, 0);
+      vector<thread> threads;
+      for(size_t c = 0; c < 10; ++c) {
+        threads.emplace_back([c, &calls] {
+          HttpClient client("localhost:8080");
+          client.request("POST", "/string", "A string", [c, &calls](shared_ptr<HttpClient::Response> response, const SimpleWeb::error_code &ec) {
+            ASSERT(!ec);
+            ASSERT(response->content.string() == "A string");
+            calls[c] = 1;
+          });
+          client.io_service->run();
+        });
+      }
+      for(auto &thread : threads)
+        thread.join();
+      for(auto call : calls)
+        ASSERT(call);
+    }
   }
 
   // Test concurrent synchronous request calls
@@ -390,7 +407,7 @@ int main() {
 
   // Test Client client's stop()
   for(size_t c = 0; c < 40; ++c) {
-    auto io_service = make_shared<asio::io_service>();
+    auto io_service = make_shared<SimpleWeb::io_context>();
     bool call = false;
     HttpClient client("localhost:8080");
     client.io_service = io_service;
@@ -410,7 +427,7 @@ int main() {
 
   // Test Client destructor that should cancel the client's request
   for(size_t c = 0; c < 40; ++c) {
-    auto io_service = make_shared<asio::io_service>();
+    auto io_service = make_shared<SimpleWeb::io_context>();
     {
       HttpClient client("localhost:8080");
       client.io_service = io_service;
@@ -431,7 +448,7 @@ int main() {
 
   // Test server destructor
   {
-    auto io_service = make_shared<asio::io_service>();
+    auto io_service = make_shared<SimpleWeb::io_context>();
     bool call = false;
     bool client_catch = false;
     {
diff --git a/tests/parse_test.cpp b/tests/parse_test.cpp
index c521b38..e739a59 100644
--- a/tests/parse_test.cpp
+++ b/tests/parse_test.cpp
@@ -147,7 +147,7 @@ int main() {
   ASSERT(fields_result1 == fields_result2 && fields_result1 == fields);
 
   auto serverTest = make_shared<ServerTest>();
-  serverTest->io_service = std::make_shared<asio::io_service>();
+  serverTest->io_service = std::make_shared<io_context>();
 
   serverTest->parse_request_test();
 
@@ -160,7 +160,7 @@ int main() {
   clientTest2->parse_response_header_test();
 
 
-  asio::io_service io_service;
+  io_context io_service;
   asio::ip::tcp::socket socket(io_service);
   SimpleWeb::Server<HTTP>::Request request(static_cast<size_t>(-1), nullptr);
   {