diff --git a/src/Npgsql/Internal/NpgsqlConnector.cs b/src/Npgsql/Internal/NpgsqlConnector.cs
index 25262b323a..16a9298b16 100644
--- a/src/Npgsql/Internal/NpgsqlConnector.cs
+++ b/src/Npgsql/Internal/NpgsqlConnector.cs
@@ -378,7 +378,7 @@ internal NpgsqlConnector(NpgsqlDataSource dataSource, NpgsqlConnection conn)
         _isKeepAliveEnabled = Settings.KeepAlive > 0;
         if (_isKeepAliveEnabled)
             _keepAliveTimer = new Timer(PerformKeepAlive, null, Timeout.Infinite, Timeout.Infinite);
-        
+
         DataReader = new NpgsqlDataReader(this);
 
         // TODO: Not just for automatic preparation anymore...
@@ -659,7 +659,7 @@ internal async Task Open(NpgsqlTimeout timeout, bool async, CancellationToken ca
                 reader.NextResult();
                 reader.Read();
             }
-                
+
             _isTransactionReadOnly = reader.GetString(0) != "off";
 
             var databaseState = UpdateDatabaseState();
@@ -876,6 +876,18 @@ async Task RawOpen(SslMode sslMode, NpgsqlTimeout timeout, bool async, Cancellat
                         certificateValidationCallback = SslVerifyFullValidation;
                     }
 
+                    var host = Host;
+
+#if !NET8_0_OR_GREATER
+                    // If the host is a valid IP address - replace it with an empty string
+                    // We do that because .NET uses targetHost argument to send SNI to the server
+                    // RFC explicitly prohibits sending an IP address so some servers might fail
+                    // This was already fixed for .NET 8
+                    // See #5543 for discussion
+                    if (IPAddress.TryParse(host, out _))
+                        host = string.Empty;
+#endif
+
                     timeout.CheckAndApply(this);
 
                     try
@@ -889,9 +901,9 @@ async Task RawOpen(SslMode sslMode, NpgsqlTimeout timeout, bool async, Cancellat
 #endif
 
                         if (async)
-                            await sslStream.AuthenticateAsClientAsync(Host, clientCertificates, sslProtocols, checkCertificateRevocation);
+                            await sslStream.AuthenticateAsClientAsync(host, clientCertificates, sslProtocols, checkCertificateRevocation);
                         else
-                            sslStream.AuthenticateAsClient(Host, clientCertificates, sslProtocols, checkCertificateRevocation);
+                            sslStream.AuthenticateAsClient(host, clientCertificates, sslProtocols, checkCertificateRevocation);
 
                         _stream = sslStream;
                     }
@@ -2076,7 +2088,7 @@ internal Exception Break(Exception reason)
             Monitor.Exit(CleanupLock);
         }
     }
-        
+
     void FullCleanup()
     {
         lock (CleanupLock)