diff --git a/include/mqtt/endpoint.hpp b/include/mqtt/endpoint.hpp
index e3ab0c5ab..8e003eebe 100644
--- a/include/mqtt/endpoint.hpp
+++ b/include/mqtt/endpoint.hpp
@@ -4796,8 +4796,8 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
     }
 
     bool handle_close_or_error(error_code ec) {
-        if (!ec) return false;
         if (connected_) {
+            if (!ec) return false;
             connected_ = false;
             mqtt_connected_ = false;
             {
@@ -4814,6 +4814,7 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
         }
         disconnect_requested_ = false;
         connect_requested_ = false;
+        if (!ec) ec = boost::system::errc::make_error_code(boost::system::errc::not_connected);
         clean_sub_unsub_inflight_on_error(ec);
         return true;
     }
@@ -5225,22 +5226,11 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
                 call_protocol_error_handlers();
                 return;
             }
-            socket_->post(
-                [
-                    self = force_move(self),
-                    session_life_keeper = force_move(session_life_keeper),
-                    buf = force_move(buf),
-                    size,
-                    handler = force_move(handler)
-                ]
-                () mutable {
-                    handler(
-                        buf.substr(0, size),
-                        buf.substr(size),
-                        force_move(session_life_keeper),
-                        force_move(self)
-                    );
-                }
+            handler(
+                buf.substr(0, size),
+                buf.substr(size),
+                force_move(session_life_keeper),
+                force_move(self)
             );
         }
     }
@@ -5285,27 +5275,17 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
             );
         }
         else {
-            socket_->post(
-               [
-                    self = force_move(self),
-                    session_life_keeper = force_move(session_life_keeper),
-                    buf = force_move(buf),
-                    handler = force_move(handler)
-               ]
-               () mutable {
-                    auto packet_id =
-                        make_packet_id<Bytes>::apply(
-                            buf.data(),
-                            std::next(buf.data(), boost::numeric_cast<buffer::difference_type>(Bytes))
-                        );
-                    buf.remove_prefix(Bytes);
-                    handler(
-                        packet_id,
-                        force_move(buf),
-                        force_move(session_life_keeper),
-                        force_move(self)
-                    );
-               }
+            auto packet_id =
+                make_packet_id<Bytes>::apply(
+                    buf.data(),
+                    std::next(buf.data(), boost::numeric_cast<buffer::difference_type>(Bytes))
+                );
+            buf.remove_prefix(Bytes);
+            handler(
+                packet_id,
+                force_move(buf),
+                force_move(session_life_keeper),
+                force_move(self)
             );
         }
     }
@@ -5409,26 +5389,13 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
             );
         }
         else {
-            socket_->post(
-                [
-                    session_life_keeper = force_move(session_life_keeper),
-                    handler = force_move(handler),
-                    buf = force_move(buf),
-                    size,
-                    multiplier,
-                    proc = force_move(proc),
-                    self = force_move(self)
-                ]
-                () mutable {
-                    proc(
-                        force_move(session_life_keeper),
-                        force_move(buf),
-                        force_move(handler),
-                        size,
-                        multiplier,
-                        force_move(self)
-                    );
-                }
+            proc(
+                force_move(session_life_keeper),
+                force_move(buf),
+                force_move(handler),
+                size,
+                multiplier,
+                force_move(self)
             );
         }
     }
@@ -5585,25 +5552,13 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
                     );
                 }
                 else {
-                    socket_->post(
-                        [
-                            this,
-                            self = force_move(self),
-                            session_life_keeper = force_move(session_life_keeper),
-                            buf = force_move(buf),
-                            handler = force_move(handler),
-                            property_length
-                        ]
-                        () mutable {
-                            process_property_id(
-                                force_move(session_life_keeper),
-                                force_move(buf),
-                                property_length,
-                                v5::properties(),
-                                force_move(handler),
-                                force_move(self)
-                            );
-                        }
+                    process_property_id(
+                        force_move(session_life_keeper),
+                        force_move(buf),
+                        property_length,
+                        v5::properties(),
+                        force_move(handler),
+                        force_move(self)
                     );
                 }
             },
@@ -5654,29 +5609,16 @@ class endpoint : public std::enable_shared_from_this<endpoint<Mutex, LockGuard,
             );
         }
         else {
-            socket_->post(
-                [
-                    this,
-                    self = force_move(self),
-                    session_life_keeper = force_move(session_life_keeper),
-                    buf = force_move(buf),
-                    props = force_move(props),
-                    handler = force_move(handler),
-                    property_length_rest
-                ]
-                () mutable {
-                    auto id = static_cast<v5::property::id>(buf.front());
-                    buf.remove_prefix(1);
-                    process_property_body(
-                        force_move(session_life_keeper),
-                        force_move(buf),
-                        id,
-                        property_length_rest - 1,
-                        force_move(props),
-                        force_move(handler),
-                        force_move(self)
-                    );
-                }
+            auto id = static_cast<v5::property::id>(buf.front());
+            buf.remove_prefix(1);
+            process_property_body(
+                force_move(session_life_keeper),
+                force_move(buf),
+                id,
+                property_length_rest - 1,
+                force_move(props),
+                force_move(handler),
+                force_move(self)
             );
         }
     }
diff --git a/test/system/CMakeLists.txt b/test/system/CMakeLists.txt
index 1d5a1ab89..9bbe337af 100644
--- a/test/system/CMakeLists.txt
+++ b/test/system/CMakeLists.txt
@@ -59,6 +59,7 @@ ENDIF ()
 IF (MQTT_TEST_7)
     LIST (APPEND check_PROGRAMS
         st_async_pubsub_2.cpp
+        st_issue_749.cpp
         st_broker_offline_message.cpp
         st_remaining_length.cpp
         st_utf8string_validate.cpp
diff --git a/test/system/st_issue_749.cpp b/test/system/st_issue_749.cpp
new file mode 100644
index 000000000..926a4d5d2
--- /dev/null
+++ b/test/system/st_issue_749.cpp
@@ -0,0 +1,86 @@
+// Copyright Takatoshi Kondo 2020
+//
+// 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 "../common/test_main.hpp"
+#include "combi_test.hpp"
+#include "checker.hpp"
+#include "test_util.hpp"
+#include "../common/global_fixture.hpp"
+
+BOOST_AUTO_TEST_SUITE(st_issue_749)
+
+using namespace MQTT_NS::literals;
+
+BOOST_AUTO_TEST_CASE( broker_assertion_fail ) {
+
+    boost::asio::io_context iocb;
+    MQTT_NS::broker::broker_t  b(iocb);
+    MQTT_NS::optional<test_server_no_tls> s;
+
+    std::promise<void> p;
+    auto f = p.get_future();
+    std::thread th(
+        [&] {
+            s.emplace(iocb, b);
+            p.set_value();
+            iocb.run();
+        }
+    );
+    f.wait();
+
+    auto finish =
+        [&] {
+            as::post(
+                iocb,
+                [&] {
+                    s->close();
+                }
+            );
+        };
+
+    std::vector<std::shared_ptr<std::thread>> client_th;
+
+    std::size_t num_clients = 10;
+
+    auto client_thread_func =
+        [] {
+            boost::asio::io_context ioc;
+
+            int publish_count = 100;
+
+            auto c1 = MQTT_NS::make_client(ioc, broker_url, broker_notls_port);
+            c1->set_clean_session(true);
+            c1->set_client_id("cid1");
+
+            c1->set_connack_handler(
+                [&c1, &publish_count]
+                (bool /*sp*/, MQTT_NS::connect_return_code /*connack_return_code*/) {
+                    std::cout << "Publish: " << publish_count << std::endl;
+                    for (std::size_t i = 0; i != 100; ++i) {
+                        c1->publish("topic1", "topic1_contents1", MQTT_NS::qos::at_most_once);
+                    }
+                    c1->disconnect();
+                    return true;
+                }
+            );
+
+            c1->connect();
+            ioc.run();
+            std::cout << "finished" << std::endl;
+        };
+
+    for (unsigned int i = 0; i != num_clients; ++i) {
+        client_th.push_back(std::make_shared<std::thread>(client_thread_func));
+    }
+
+    for(auto& th: client_th) {
+        th->join();
+    }
+    finish();
+    th.join();
+}
+
+BOOST_AUTO_TEST_SUITE_END()