diff --git a/Source/HiveMQtt/Client/HiveMQClient.cs b/Source/HiveMQtt/Client/HiveMQClient.cs
index 426d0e1..ceee2ed 100644
--- a/Source/HiveMQtt/Client/HiveMQClient.cs
+++ b/Source/HiveMQtt/Client/HiveMQClient.cs
@@ -234,9 +234,14 @@ public async Task<PublishResult> PublishAsync(MQTT5PublishMessage message, Cance
             throw new HiveMQttClientException("Retained messages are not supported by the broker");
         }
 
-        if (message.QoS.HasValue && this.Connection.ConnectionProperties.MaximumQoS.HasValue &&
+        if (message.QoS.HasValue && this.Connection?.ConnectionProperties?.MaximumQoS.HasValue == true &&
             (ushort)message.QoS.Value > this.Connection.ConnectionProperties.MaximumQoS.Value)
         {
+            if (this.Connection == null)
+            {
+                throw new HiveMQttClientException("Connection is not available");
+            }
+
             Logger.Debug($"Reducing message QoS from {message.QoS} to broker enforced maximum of {this.Connection.ConnectionProperties.MaximumQoS}");
             message.QoS = (QualityOfService)this.Connection.ConnectionProperties.MaximumQoS.Value;
         }
@@ -247,12 +252,17 @@ public async Task<PublishResult> PublishAsync(MQTT5PublishMessage message, Cance
             var publishPacket = new PublishPacket(message, 0);
             Logger.Trace($"Queuing QoS 0 publish packet for send: {publishPacket.GetType().Name}");
 
-            this.Connection.OutgoingPublishQueue.Enqueue(publishPacket);
+            this.Connection?.OutgoingPublishQueue.Enqueue(publishPacket);
             return new PublishResult(publishPacket.Message);
         }
         else if (message.QoS == QualityOfService.AtLeastOnceDelivery)
         {
             // QoS 1: Acknowledged Delivery
+            if (this.Connection == null)
+            {
+                throw new HiveMQttClientException("Connection is not available");
+            }
+
             var packetIdentifier = await this.Connection.PacketIDManager.GetAvailablePacketIDAsync().ConfigureAwait(false);
             var publishPacket = new PublishPacket(message, (ushort)packetIdentifier);
             PubAckPacket pubAckPacket;
@@ -278,6 +288,11 @@ public async Task<PublishResult> PublishAsync(MQTT5PublishMessage message, Cance
         else if (message.QoS == QualityOfService.ExactlyOnceDelivery)
         {
             // QoS 2: Assured Delivery
+            if (this.Connection == null)
+            {
+                throw new HiveMQttClientException("Connection is not available");
+            }
+
             var packetIdentifier = await this.Connection.PacketIDManager.GetAvailablePacketIDAsync().ConfigureAwait(false);
             var publishPacket = new PublishPacket(message, (ushort)packetIdentifier);
             var publishResult = new PublishResult(publishPacket.Message);
@@ -406,6 +421,11 @@ public async Task<SubscribeResult> SubscribeAsync(SubscribeOptions options)
         // Fire the corresponding event
         this.BeforeSubscribeEventLauncher(options);
 
+        if (this.Connection == null)
+        {
+            throw new HiveMQttClientException("Connection is not available");
+        }
+
         // FIXME: We should only ever have one subscribe in flight at any time (for now)
         // Construct the MQTT Subscribe packet
         var packetIdentifier = await this.Connection.PacketIDManager.GetAvailablePacketIDAsync().ConfigureAwait(false);
diff --git a/Source/HiveMQtt/Client/HiveMQClientEvents.cs b/Source/HiveMQtt/Client/HiveMQClientEvents.cs
index 894775c..d854457 100644
--- a/Source/HiveMQtt/Client/HiveMQClientEvents.cs
+++ b/Source/HiveMQtt/Client/HiveMQClientEvents.cs
@@ -262,6 +262,7 @@ internal virtual void OnMessageReceivedEventLauncher(PublishPacket packet)
                         }
                     }, TaskScheduler.Default);
             }
+
             messageHandled = true;
         }