diff --git a/test/ServerComparison.FunctionalTests/ResponseTests.cs b/test/ServerComparison.FunctionalTests/ResponseTests.cs
index b106f38fb7..d7b14ce3b0 100644
--- a/test/ServerComparison.FunctionalTests/ResponseTests.cs
+++ b/test/ServerComparison.FunctionalTests/ResponseTests.cs
@@ -34,9 +34,9 @@ namespace ServerComparison.FunctionalTests
             return ResponseFormats(serverType, runtimeFlavor, architecture, applicationBaseUrl, CheckContentLengthAsync);
         }
 
-        // [ConditionalTheory]
-        // [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
-        // TODO: Not supported [InlineData(ServerType.IISExpress, RuntimeFlavor.CoreClr, RuntimeArchitecture.x86, "http://localhost:5071/")]
+        [ConditionalTheory]
+        [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
+        [InlineData(ServerType.IISExpress, RuntimeFlavor.CoreClr, RuntimeArchitecture.x86, "http://localhost:5071/")]
         // https://github.com/aspnet/Helios/issues/148
         // TODO: Chunks anyways [InlineData(ServerType.WebListener, RuntimeFlavor.Clr, RuntimeArchitecture.x86, "http://localhost:5073/")]
         // https://github.com/aspnet/WebListener/issues/113
@@ -155,8 +155,8 @@ namespace ServerComparison.FunctionalTests
                 var response = await client.GetAsync("connectionclose");
                 responseText = await response.Content.ReadAsStringAsync();
                 Assert.Equal("Connnection Close", responseText);
-                Assert.Null(response.Headers.TransferEncodingChunked);
                 Assert.True(response.Headers.ConnectionClose, "/connectionclose, closed?");
+                Assert.Null(response.Headers.TransferEncodingChunked);
                 Assert.Null(GetContentLength(response));
             }
             catch (XunitException)
diff --git a/test/ServerComparison.TestSites/StartupResponses.cs b/test/ServerComparison.TestSites/StartupResponses.cs
index 563fdd0894..67fc0800ab 100644
--- a/test/ServerComparison.TestSites/StartupResponses.cs
+++ b/test/ServerComparison.TestSites/StartupResponses.cs
@@ -25,10 +25,11 @@ namespace ServerComparison.TestSites
 
             app.Map("/connectionclose", subApp =>
             {
-                subApp.Run(context =>
+                subApp.Run(async context =>
                 {
                     context.Response.Headers[HeaderNames.Connection] = "close";
-                    return context.Response.WriteAsync("Connnection Close");
+                    await context.Response.WriteAsync("Connnection Close");
+                    await context.Response.Body.FlushAsync(); // Bypass IIS write-behind buffering
                 });
             });