diff --git a/Source/MQTTnet/Server/Internal/MqttClientSession.cs b/Source/MQTTnet/Server/Internal/MqttClientSession.cs
index 291b3e5a..a943f5ad 100644
--- a/Source/MQTTnet/Server/Internal/MqttClientSession.cs
+++ b/Source/MQTTnet/Server/Internal/MqttClientSession.cs
@@ -8,11 +8,6 @@ namespace MQTTnet.Server.Internal
     {
         readonly DateTime _createdTimestamp = DateTime.UtcNow;
 
-        /// <summary>
-        /// Session should persist if CleanSession was set to false (Mqtt3) or if SessionExpiryInterval != 0 (Mqtt5)
-        /// </summary>
-        readonly bool _isPersistent;
-
         public MqttClientSession(
             string clientId,
             IDictionary<object, object> items,
@@ -24,17 +19,19 @@ namespace MQTTnet.Server.Internal
         {
             ClientId = clientId ?? throw new ArgumentNullException(nameof(clientId));
             Items = items ?? throw new ArgumentNullException(nameof(items));
-
+            IsPersistent = isPersistent;
             SubscriptionsManager = new MqttClientSubscriptionsManager(this, serverOptions, eventDispatcher, retainedMessagesManager);
             ApplicationMessagesQueue = new MqttClientSessionApplicationMessagesQueue(serverOptions);
-            _isPersistent = isPersistent;
         }
 
         public string ClientId { get; }
 
         public bool IsCleanSession { get; set; } = true;
 
-        public bool IsPersistent => _isPersistent;
+        /// <summary>
+        /// Session should persist if CleanSession was set to false (Mqtt3) or if SessionExpiryInterval != 0 (Mqtt5)
+        /// </summary>
+        public bool IsPersistent { get; set; }
 
         public MqttApplicationMessage WillMessage { get; set; }
 
diff --git a/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs b/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs
index 8831a05b..471e9df8 100644
--- a/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs
+++ b/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs
@@ -507,7 +507,7 @@ namespace MQTTnet.Server.Internal
                 // in each time it connects.
 
                 // Persist if SessionExpiryInterval != 0, but may start with a clean session
-                sessionShouldPersist = context.SessionExpiryInterval != 0;
+                sessionShouldPersist = context.SessionExpiryInterval.GetValueOrDefault() != 0;
             }
             else
             {
@@ -540,6 +540,8 @@ namespace MQTTnet.Server.Internal
                         else
                         {
                             _logger.Verbose("Reusing existing session of client '{0}'.", connectPacket.ClientId);
+                            // Session persistence could change for MQTT 5 clients that reconnect with different SessionExpiryInterval
+                            session.IsPersistent = sessionShouldPersist;
                             connAckPacket.IsSessionPresent = true;
                         }
                     }
diff --git a/Tests/MQTTnet.Core.Tests/MQTTv5/Server_Tests.cs b/Tests/MQTTnet.Core.Tests/MQTTv5/Server_Tests.cs
index 18fde518..ce015b18 100644
--- a/Tests/MQTTnet.Core.Tests/MQTTv5/Server_Tests.cs
+++ b/Tests/MQTTnet.Core.Tests/MQTTv5/Server_Tests.cs
@@ -51,15 +51,8 @@ namespace MQTTnet.Tests.MQTTv5
                 const string ClientId = "Client1";
 
                 // Create client without clean session and long session expiry interval
-
-                var client1 = await testEnvironment.ConnectClient(o => o
-                    .WithProtocolVersion(MqttProtocolVersion.V500)
-                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
-                    .WithSessionExpiryInterval(9999)
-                    .WithCleanSession(false)
-                    .WithClientId(ClientId)
-                    .Build()
-                );
+                var options1 = CreateClientOptions(testEnvironment, ClientId, false, 9999);
+                var client1 = await testEnvironment.ConnectClient(options1);
 
                 // Disconnect; empty session should remain on server
 
@@ -72,16 +65,8 @@ namespace MQTTnet.Tests.MQTTv5
                 // Reconnect the same client ID to existing session
 
                 var client2 = testEnvironment.CreateClient();
-                var options = testEnvironment.Factory.CreateClientOptionsBuilder()
-                    .WithProtocolVersion(MqttProtocolVersion.V500)
-                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
-                    .WithSessionExpiryInterval(9999)
-                    .WithCleanSession(false)
-                    .WithClientId(ClientId)
-                    .Build();
-
-
-                var result = await client2.ConnectAsync(options).ConfigureAwait(false);
+                var options2 = CreateClientOptions(testEnvironment, ClientId, false, 9999);
+                var result = await client2.ConnectAsync(options2).ConfigureAwait(false);
 
                 await client2.DisconnectAsync();
 
@@ -90,5 +75,111 @@ namespace MQTTnet.Tests.MQTTv5
                 Assert.IsTrue(result.IsSessionPresent, "Session not present");
             }
         }
+
+        [TestMethod]
+        public async Task Connect_with_Undefined_SessionExpiryInterval()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                // Create server with persistent sessions enabled
+
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                const string ClientId = "Client1";
+
+                // Create client without clean session and NO session expiry interval,
+                // that means, the session should not persist
+
+                var options1 = CreateClientOptions(testEnvironment, ClientId, false, null);
+                var client1 = await testEnvironment.ConnectClient(options1);
+
+                // Disconnect; no session should remain on server because the session expiry interval was undefined
+
+                await client1.DisconnectAsync();
+
+                // Simulate some time delay between connections
+
+                await Task.Delay(1000);
+
+                // Reconnect the same client ID to existing session
+
+                var client2 = testEnvironment.CreateClient();
+                var options2 = CreateClientOptions(testEnvironment, ClientId, false, 9999);
+                var result = await client2.ConnectAsync(options2).ConfigureAwait(false);
+
+                await client2.DisconnectAsync();
+
+                // Session should not be present
+
+                Assert.IsTrue(!result.IsSessionPresent, "Session is present when it should not");
+            }
+        }
+
+
+        [TestMethod]
+        public async Task Reconnect_with_different_SessionExpiryInterval()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                // Create server with persistent sessions enabled
+
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                const string ClientId = "Client1";
+
+                // Create client with clean session and session expiry interval > 0
+
+                var options = CreateClientOptions(testEnvironment, ClientId, true, 9999);
+                var client1 = await testEnvironment.ConnectClient(options);
+
+                // Disconnect; session should remain on server
+
+                await client1.DisconnectAsync();
+
+                // Simulate some time delay between connections
+
+                await Task.Delay(1000);
+
+                // Reconnect the same client ID to the existing session but leave session expiry interval undefined this time.
+                // Session should be present because the client1 connection had SessionExpiryInterval > 0
+
+                var client2 = testEnvironment.CreateClient();
+                var options2 = CreateClientOptions(testEnvironment, ClientId, false, null);
+                var result2 = await client2.ConnectAsync(options2).ConfigureAwait(false);
+
+                await client2.DisconnectAsync();
+
+                Assert.IsTrue(result2.IsSessionPresent, "Session is not present when it should");
+
+                // Simulate some time delay between connections
+
+                await Task.Delay(1000);
+
+                // Reconnect the same client ID.
+                // No session should be present because the previous session expiry interval was undefined for the client2 connection
+
+                var client3 = testEnvironment.CreateClient();
+                var options3 = CreateClientOptions(testEnvironment, ClientId, false, null);
+                var result3 = await client2.ConnectAsync(options3).ConfigureAwait(false);
+
+                await client3.DisconnectAsync();
+
+                // Session should be present
+
+                Assert.IsTrue(!result3.IsSessionPresent, "Session is present when it should not");
+
+            }
+        }
+
+        IMqttClientOptions CreateClientOptions(TestEnvironment testEnvironment, string clientId, bool cleanSession, uint? sessionExpiryInterval)
+        {
+            return testEnvironment.Factory.CreateClientOptionsBuilder()
+                .WithProtocolVersion(MqttProtocolVersion.V500)
+                .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                .WithSessionExpiryInterval(sessionExpiryInterval)
+                .WithCleanSession(cleanSession)
+                .WithClientId(clientId)
+                .Build();
+        }
     }
 }