diff --git a/src/Renci.SshNet/Security/KeyExchange.cs b/src/Renci.SshNet/Security/KeyExchange.cs
index 05b1459c3..834b71e24 100644
--- a/src/Renci.SshNet/Security/KeyExchange.cs
+++ b/src/Renci.SshNet/Security/KeyExchange.cs
@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Security.Cryptography;
 
@@ -530,9 +529,7 @@ protected void SendMessage(Message message)
         /// </returns>
         private byte[] GenerateSessionKey(byte[] sharedKey, byte[] exchangeHash, byte[] key, int size)
         {
-            var result = new List<byte>(key);
-
-            while (size > result.Count)
+            while (key.Length < size)
             {
                 var sessionKeyAdjustment = new SessionKeyAdjustment
                 {
@@ -541,10 +538,10 @@ private byte[] GenerateSessionKey(byte[] sharedKey, byte[] exchangeHash, byte[]
                     Key = key,
                 };
 
-                result.AddRange(Hash(sessionKeyAdjustment.GetBytes()));
+                key = key.Concat(Hash(sessionKeyAdjustment.GetBytes()));
             }
 
-            return result.ToArray();
+            return key;
         }
 
         /// <summary>
diff --git a/test/Renci.SshNet.IntegrationTests/HmacTests.cs b/test/Renci.SshNet.IntegrationTests/HmacTests.cs
index 261b17a1a..e33f3fa8a 100644
--- a/test/Renci.SshNet.IntegrationTests/HmacTests.cs
+++ b/test/Renci.SshNet.IntegrationTests/HmacTests.cs
@@ -40,6 +40,22 @@ public void HmacSha2_512()
             DoTest(MessageAuthenticationCodeAlgorithm.HmacSha2_512);
         }
 
+        [TestMethod]
+        public void HmacSha2_512_ShortKexOutput()
+        {
+            _remoteSshdConfig.ClearMessageAuthenticationCodeAlgorithms()
+                             .AddMessageAuthenticationCodeAlgorithm(MessageAuthenticationCodeAlgorithm.HmacSha2_512)
+                             .ClearKeyExchangeAlgorithms()
+                             .AddKeyExchangeAlgorithm(KeyExchangeAlgorithm.DiffieHellmanGroupExchangeSha1)
+                             .Update()
+                             .Restart();
+
+            using (var client = new SshClient(_connectionInfoFactory.Create()))
+            {
+                client.Connect();
+                client.Disconnect();
+            }
+        }
 
         [TestMethod]
         public void HmacSha1_Etm()