diff --git a/Build/MQTTnet.nuspec b/Build/MQTTnet.nuspec
index 10da9e58..1433105e 100644
--- a/Build/MQTTnet.nuspec
+++ b/Build/MQTTnet.nuspec
@@ -13,9 +13,11 @@
     <releaseNotes>* [Core] Performance optimizations.
 * [Client] Added support for proxies when using web socket connections (thanks to PitySOFT).
 * [Client] Refactored TLS parameter usage and added more parameters (thanks to PitySOFT).
+* [Client] Fixed a deadlock when clients are disconnecting (thanks to @JanEggers).
 * [Server] Fixed an issue in client keep alive checks (thanks to @jenscski).
 * [Server] Changed the order of _ClientConnected_ and _ClientDisconnected_ events so that _ClientConnected_ is fired at first (thanks to @jenscski).
 * [Server] Fixed an iussue which lets the server stop processing messages when using the application message interceptor (thanks to @alamsor).
+* [Server] Fixed a deadlock when clients are disconnecting (thanks to @JanEggers).
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
diff --git a/Source/MQTTnet/Server/MqttClientSession.cs b/Source/MQTTnet/Server/MqttClientSession.cs
index fe586636..de3a7a48 100644
--- a/Source/MQTTnet/Server/MqttClientSession.cs
+++ b/Source/MQTTnet/Server/MqttClientSession.cs
@@ -81,13 +81,16 @@ namespace MQTTnet.Server
             try
             {
                 _adapter = adapter;
+
                 adapter.ReadingPacketStarted += OnAdapterReadingPacketStarted;
                 adapter.ReadingPacketCompleted += OnAdapterReadingPacketCompleted;
 
                 _cancellationTokenSource = new CancellationTokenSource();
 
                 //woraround for https://github.com/dotnet/corefx/issues/24430
-                _cleanupHandle = _cancellationTokenSource.Token.Register(() => Cleanup());
+#pragma warning disable 4014
+                _cleanupHandle = _cancellationTokenSource.Token.Register(() => CleanupAsync());
+#pragma warning restore 4014
                 //endworkaround
 
                 _wasCleanDisconnect = false;
@@ -131,7 +134,7 @@ namespace MQTTnet.Server
             }
             finally
             {
-                await Cleanup().ConfigureAwait(false);
+                await CleanupAsync().ConfigureAwait(false);
 
                 _cleanupHandle?.Dispose();
                 _cleanupHandle = null;
@@ -141,11 +144,11 @@ namespace MQTTnet.Server
             }
         }
 
-        private async Task Cleanup()
+        private async Task CleanupAsync()
         {
+            var adapter = _adapter;
             try
             {
-                var adapter = _adapter;
                 if (adapter == null)
                 {
                     return;
@@ -155,13 +158,17 @@ namespace MQTTnet.Server
 
                 adapter.ReadingPacketStarted -= OnAdapterReadingPacketStarted;
                 adapter.ReadingPacketCompleted -= OnAdapterReadingPacketCompleted;
+
                 await adapter.DisconnectAsync(_options.DefaultCommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
-                adapter.Dispose();
             }
             catch (Exception exception)
             {
                 _logger.Error(exception, exception.Message);
             }
+            finally
+            {
+                adapter?.Dispose();
+            }
         }
 
         public void Stop(MqttClientDisconnectType type)