diff --git a/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Driver.cs b/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Driver.cs
index ca1fa40..d93047a 100644
--- a/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Driver.cs	
+++ b/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Driver.cs	
@@ -15,7 +15,7 @@ public class Driver
         internal static List<int> UsedPorts = new List<int>();
 
         internal Websocket.Client.WebsocketClient ClientWebSocket;
-        internal Dictionary<Guid, Action<JObject>> Callbacks;
+        internal TSafeDictionary<Guid, Action<JObject>> Callbacks;
         internal bool Inited = false;
         internal ZWaveOptions Options;
         internal const string FWUSAPIKey = "921f8000486fcc2744721cfc747aab2db8fc025b5d487cbf2eba76e88ff6f79a064644bf";
@@ -574,7 +574,7 @@ public Driver(Uri Server, int SchemaVersion = 0, int ServerErrorThrottleTime = 1
                 _schemaVersion = SchemaVersion;
             }
 
-            Callbacks = new Dictionary<Guid, Action<JObject>>();
+            Callbacks = new TSafeDictionary<Guid, Action<JObject>>();
             MapEvents();
             
             this.WSAddress = Server;
@@ -607,7 +607,7 @@ public Driver(string SerialPort, ZWaveOptions Options, int ServerCommunicationPo
             settings.Converters.Add(new ZWJSSJsonConverter(this));
             _jsonSerializer = JsonSerializer.Create(settings);
 
-            Callbacks = new Dictionary<Guid, Action<JObject>>();
+            Callbacks = new TSafeDictionary<Guid, Action<JObject>>();
             MapEvents();
             
             this.SerialPort = SerialPort;
diff --git a/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Structures.cs b/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Structures.cs
index 92347fd..06011fa 100644
--- a/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Structures.cs	
+++ b/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Structures.cs	
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Dynamic;
 using System.IO;
@@ -579,4 +580,45 @@ internal FirmwareUpdate() { }
         public string filename { get; internal set; }
         public int? firmwareTarget { get; internal set; }
     }
+
+    /// <summary>
+    /// Thread-safe Dictionary
+    /// </summary>
+    /// <remarks>
+    /// ConcurrentDictionary wrapper class exposing a partial 
+    /// "Dictionary-like" interface for use in this application.
+    /// </remarks>
+    public class TSafeDictionary<K, V> {
+
+        private ConcurrentDictionary<K, V> _dictionary 
+            = new ConcurrentDictionary<K, V>();
+
+        public V this[K key] {
+            get {
+                if (!_dictionary.TryGetValue(key, out V value)) {
+                    throw new KeyNotFoundException();
+                }
+                return value;
+            }
+            private set { }
+        }
+
+        public ICollection<K> Keys {
+            get { return (_dictionary.Keys); }
+        }
+
+        public void Add(K key, V callback) {
+            if (!_dictionary.TryAdd(key, callback)) {
+                throw new ArgumentException();
+            }
+        }
+
+        public Boolean Remove(K key) {
+            return _dictionary.TryRemove(key, out _);
+        }
+
+        public Boolean ContainsKey(K key) {
+            return _dictionary.ContainsKey(key);
+        }
+    }
 }
diff --git a/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Websocket.Client/WebsocketClient.Sending.cs b/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Websocket.Client/WebsocketClient.Sending.cs
index 1967941..d4b0d83 100644
--- a/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Websocket.Client/WebsocketClient.Sending.cs	
+++ b/Visual Studio Projects/ZWaveJS.NET/ZWaveJS.NET/Websocket.Client/WebsocketClient.Sending.cs	
@@ -58,6 +58,12 @@ public void Send(ArraySegment<byte> message)
             _messagesBinaryToSendQueue.Writer.TryWrite(message);
         }
 
+        /// <summary>
+        /// Synchronize the SendInstant calls to avoid
+        /// the documented issue with simultaneous usage.
+        /// </summary>
+        private Object _sendInstantLock = new Object();
+
         /// <summary>
         /// Send text message to the websocket channel. 
         /// It doesn't use a sending queue, 
@@ -69,7 +75,9 @@ public Task SendInstant(string message)
         {
             Validations.Validations.ValidateInput(message, nameof(message));
 
-            return SendInternalSynchronized(message);
+            lock (_sendInstantLock) {
+                return SendInternalSynchronized(message);
+            }
         }
 
         /// <summary>
@@ -81,7 +89,9 @@ public Task SendInstant(string message)
         /// <param name="message">Message to be sent</param>
         public Task SendInstant(byte[] message)
         {
-            return SendInternalSynchronized(new ArraySegment<byte>(message));
+            lock (_sendInstantLock) {
+                return SendInternalSynchronized(new ArraySegment<byte>(message));
+            }
         }
 
         /// <summary>