diff --git a/src/Microsoft.AspNetCore.Server.IIS/Core/IISHttpContext.cs b/src/Microsoft.AspNetCore.Server.IIS/Core/IISHttpContext.cs
index a9eecba00b..45848183ba 100644
--- a/src/Microsoft.AspNetCore.Server.IIS/Core/IISHttpContext.cs
+++ b/src/Microsoft.AspNetCore.Server.IIS/Core/IISHttpContext.cs
@@ -318,29 +318,23 @@ namespace Microsoft.AspNetCore.Server.IIS.Core
             {
                 var headerValues = headerPair.Value;
                 var knownHeaderIndex = HttpApiTypes.HTTP_RESPONSE_HEADER_ID.IndexOfKnownHeader(headerPair.Key);
-                if (knownHeaderIndex == -1)
+                for (var i = 0; i < headerValues.Count; i++)
                 {
-                    var headerNameBytes = Encoding.UTF8.GetBytes(headerPair.Key);
-                    for (var i = 0; i < headerValues.Count; i++)
+                    var isFirst = i == 0;
+                    var headerValueBytes = Encoding.UTF8.GetBytes(headerValues[i]);
+                    fixed (byte* pHeaderValue = headerValueBytes)
                     {
-                        var headerValueBytes = Encoding.UTF8.GetBytes(headerValues[i]);
-                        fixed (byte* pHeaderName = headerNameBytes)
+                        if (knownHeaderIndex == -1)
                         {
-                            fixed (byte* pHeaderValue = headerValueBytes)
+                            var headerNameBytes = Encoding.UTF8.GetBytes(headerPair.Key);
+                            fixed (byte* pHeaderName = headerNameBytes)
                             {
-                                NativeMethods.HttpResponseSetUnknownHeader(_pInProcessHandler, pHeaderName, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: false);
+                                NativeMethods.HttpResponseSetUnknownHeader(_pInProcessHandler, pHeaderName, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: isFirst);
                             }
                         }
-                    }
-                }
-                else
-                {
-                    for (var i = 0; i < headerValues.Count; i++)
-                    {
-                        var headerValueBytes = Encoding.UTF8.GetBytes(headerValues[i]);
-                        fixed (byte* pHeaderValue = headerValueBytes)
+                        else
                         {
-                            NativeMethods.HttpResponseSetKnownHeader(_pInProcessHandler, knownHeaderIndex, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: false);
+                            NativeMethods.HttpResponseSetKnownHeader(_pInProcessHandler, knownHeaderIndex, pHeaderValue, (ushort)headerValueBytes.Length, fReplace: isFirst);
                         }
                     }
                 }
diff --git a/test/Common.FunctionalTests/Inprocess/ResponseHeaderTests.cs b/test/Common.FunctionalTests/Inprocess/ResponseHeaderTests.cs
index 3f433b155f..fec5c227ec 100644
--- a/test/Common.FunctionalTests/Inprocess/ResponseHeaderTests.cs
+++ b/test/Common.FunctionalTests/Inprocess/ResponseHeaderTests.cs
@@ -74,5 +74,12 @@ namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests
             // ReadAsStringAsync returns empty string for empty results
             Assert.Equal(body ?? string.Empty, await response.Content.ReadAsStringAsync());
         }
+
+        [ConditionalFact]
+        public async Task ServerHeaderIsOverriden()
+        {
+            var response = await _fixture.Client.GetAsync("OverrideServer");
+            Assert.Equal("MyServer/7.8", response.Headers.Server.Single().Product.ToString());
+        }
     }
 }
diff --git a/test/Common.Tests/Utilities/TestConnections.cs b/test/Common.Tests/Utilities/TestConnections.cs
index 3364a0e021..3b7a870cf3 100644
--- a/test/Common.Tests/Utilities/TestConnections.cs
+++ b/test/Common.Tests/Utilities/TestConnections.cs
@@ -62,18 +62,15 @@ namespace Microsoft.AspNetCore.Server.IntegrationTesting
 
         public async Task Send(params string[] lines)
         {
-            var text = string.Join("\r\n", lines);
-            var writer = new StreamWriter(_stream, Encoding.GetEncoding("iso-8859-1"));
-            for (var index = 0; index < text.Length; index++)
+            var bytes = Encoding.ASCII.GetBytes(string.Join("\r\n", lines));
+
+            for (var index = 0; index < bytes.Length; index++)
             {
-                var ch = text[index];
-                writer.Write(ch);
-                await writer.FlushAsync().ConfigureAwait(false);
+                await _stream.WriteAsync(bytes, index, 1).ConfigureAwait(false);
+                await _stream.FlushAsync().ConfigureAwait(false);
                 // Re-add delay to help find socket input consumption bugs more consistently
                 //await Task.Delay(TimeSpan.FromMilliseconds(5));
             }
-            await writer.FlushAsync().ConfigureAwait(false);
-            await _stream.FlushAsync().ConfigureAwait(false);
         }
 
         public async Task<int> ReadCharAsync()
diff --git a/test/IIS.Tests/ClientDisconnectTests.cs b/test/IIS.Tests/ClientDisconnectTests.cs
index ee55959a93..9c8855be47 100644
--- a/test/IIS.Tests/ClientDisconnectTests.cs
+++ b/test/IIS.Tests/ClientDisconnectTests.cs
@@ -206,6 +206,7 @@ namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests
         [ConditionalFact]
         public async Task ReaderThrowsResetExceptionOnInvalidBody()
         {
+            var requestStartedCompletionSource = CreateTaskCompletionSource();
             var requestCompletedCompletionSource = CreateTaskCompletionSource();
 
             Exception exception = null;
@@ -213,6 +214,7 @@ namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests
             var data = new byte[1024];
             using (var testServer = await TestServer.Create(async ctx =>
             {
+                requestStartedCompletionSource.SetResult(true);
                 try
                 {
                     await ctx.Request.Body.ReadAsync(data);
@@ -233,10 +235,19 @@ namespace Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests
                         "Host: localhost",
                         "Connection: close",
                         "",
-                        "ZZZ",
                         "");
-                    await requestCompletedCompletionSource.Task.DefaultTimeout();
+
+                    await requestStartedCompletionSource.Task;
+                    await connection.Send(
+                        "ZZZZZZZZZZZZZ");
+
+                    await connection.Receive(
+                        "HTTP/1.1 400 Bad Request",
+                        ""
+                        );
+
                 }
+                await requestCompletedCompletionSource.Task.DefaultTimeout();
             }
 
             Assert.IsType<ConnectionResetException>(exception);
diff --git a/test/WebSites/shared/SharedStartup/Startup.shared.cs b/test/WebSites/shared/SharedStartup/Startup.shared.cs
index bf9e3bb7fd..375902faea 100644
--- a/test/WebSites/shared/SharedStartup/Startup.shared.cs
+++ b/test/WebSites/shared/SharedStartup/Startup.shared.cs
@@ -82,5 +82,11 @@ namespace TestSite
             }
             await context.Response.WriteAsync(_applicationInitializationCalled.ToString());
         }
+
+        public Task OverrideServer(HttpContext context)
+        {
+            context.Response.Headers["Server"] = "MyServer/7.8";
+            return Task.CompletedTask;
+        }
     }
 }