diff --git a/Source/MQTTnet/Client/Connecting/MqttClientAuthenticateResult.cs b/Source/MQTTnet/Client/Connecting/MqttClientAuthenticateResult.cs
index f7ff7253..7419fae0 100644
--- a/Source/MQTTnet/Client/Connecting/MqttClientAuthenticateResult.cs
+++ b/Source/MQTTnet/Client/Connecting/MqttClientAuthenticateResult.cs
@@ -27,7 +27,7 @@ namespace MQTTnet.Client.Connecting
 
         public ushort? ReceiveMaximum { get; set; }
         
-        public MqttQualityOfServiceLevel? MaximumQoS { get; set; }
+        public MqttQualityOfServiceLevel MaximumQoS { get; set; }
 
         public string ResponseInformation { get; set; }
 
diff --git a/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs b/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs
index b5d7103d..7f9bd92f 100644
--- a/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs
+++ b/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs
@@ -93,7 +93,7 @@ namespace MQTTnet.Formatter.V5
                 MaximumPacketSize = connAckPacket.Properties?.MaximumPacketSize,
                 ReasonString = connAckPacket.Properties?.ReasonString,
                 ReceiveMaximum = connAckPacket.Properties?.ReceiveMaximum,
-                MaximumQoS = connAckPacket.Properties?.MaximumQoS,
+                MaximumQoS = connAckPacket.Properties?.MaximumQoS ?? MqttQualityOfServiceLevel.ExactlyOnce,
                 ResponseInformation = connAckPacket.Properties?.ResponseInformation,
                 TopicAliasMaximum = connAckPacket.Properties?.TopicAliasMaximum,
                 ServerReference = connAckPacket.Properties?.ServerReference,
diff --git a/Source/MQTTnet/Formatter/V5/MqttV500PropertiesReader.cs b/Source/MQTTnet/Formatter/V5/MqttV500PropertiesReader.cs
index 3282dbda..bb8beace 100644
--- a/Source/MQTTnet/Formatter/V5/MqttV500PropertiesReader.cs
+++ b/Source/MQTTnet/Formatter/V5/MqttV500PropertiesReader.cs
@@ -89,6 +89,7 @@ namespace MQTTnet.Formatter.V5
             {
                 throw new MqttProtocolViolationException($"Unexpected Maximum QoS value: {value}");
             }
+            
             return (MqttQualityOfServiceLevel)value;
         }