diff --git a/Source/MQTTnet/Server/MqttClientSessionsManager.cs b/Source/MQTTnet/Server/MqttClientSessionsManager.cs
index 2c3202bb..bec93db6 100644
--- a/Source/MQTTnet/Server/MqttClientSessionsManager.cs
+++ b/Source/MQTTnet/Server/MqttClientSessionsManager.cs
@@ -1,4 +1,4 @@
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
@@ -21,7 +21,7 @@ namespace MQTTnet.Server
     {
         readonly BlockingCollection<MqttPendingApplicationMessage> _messageQueue = new BlockingCollection<MqttPendingApplicationMessage>();
 
-        readonly object _createConnectionSyncRoot = new object();
+        readonly AsyncLock _createConnectionSyncRoot = new AsyncLock();
         readonly Dictionary<string, MqttClientConnection> _connections = new Dictionary<string, MqttClientConnection>();
         readonly Dictionary<string, MqttClientSession> _sessions = new Dictionary<string, MqttClientSession>();
 
@@ -98,7 +98,7 @@ namespace MQTTnet.Server
                     return;
                 }
 
-                var connection = CreateClientConnection(connectPacket, connectionValidatorContext, channelAdapter);
+                var connection = await CreateClientConnectionAsync(connectPacket, connectionValidatorContext, channelAdapter).ConfigureAwait(false);
                 await _eventDispatcher.SafeNotifyClientConnectedAsync(connectPacket.ClientId).ConfigureAwait(false);
                 await connection.RunAsync().ConfigureAwait(false);
             }
@@ -387,9 +387,12 @@ namespace MQTTnet.Server
             return context;
         }
 
-        MqttClientConnection CreateClientConnection(MqttConnectPacket connectPacket, MqttConnectionValidatorContext connectionValidatorContext, IMqttChannelAdapter channelAdapter)
+        async Task<MqttClientConnection> CreateClientConnectionAsync(MqttConnectPacket connectPacket, MqttConnectionValidatorContext connectionValidatorContext, IMqttChannelAdapter channelAdapter)
         {
-            lock (_createConnectionSyncRoot)
+            MqttClientConnection existingConnection;
+            MqttClientConnection connection;
+
+            using (await _createConnectionSyncRoot.WaitAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 MqttClientSession session;
                 lock (_sessions)
@@ -415,8 +418,6 @@ namespace MQTTnet.Server
                     _sessions[connectPacket.ClientId] = session;
                 }
 
-                MqttClientConnection existingConnection;
-                MqttClientConnection connection;
                 lock (_connections)
                 {
                     _connections.TryGetValue(connectPacket.ClientId, out existingConnection);
@@ -425,10 +426,13 @@ namespace MQTTnet.Server
                     _connections[connectPacket.ClientId] = connection;
                 }
 
-                existingConnection?.StopAsync(MqttClientDisconnectReason.SessionTakenOver).GetAwaiter().GetResult();
-
-                return connection;
+                if (existingConnection != null)
+                {
+                    await existingConnection.StopAsync(MqttClientDisconnectReason.SessionTakenOver).ConfigureAwait(false);
+                }
             }
+
+            return connection;
         }
 
         async Task<MqttApplicationMessageInterceptorContext> InterceptApplicationMessageAsync(IMqttServerApplicationMessageInterceptor interceptor, MqttClientConnection clientConnection, MqttApplicationMessage applicationMessage)