diff --git a/src/Hosting/TestHost/src/WebSocketClient.cs b/src/Hosting/TestHost/src/WebSocketClient.cs
index d312c0ebbd..9f3e0500be 100644
--- a/src/Hosting/TestHost/src/WebSocketClient.cs
+++ b/src/Hosting/TestHost/src/WebSocketClient.cs
@@ -4,12 +4,14 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Net.WebSockets;
 using System.Security.Cryptography;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
+using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNetCore.TestHost
 {
@@ -72,10 +74,15 @@ namespace Microsoft.AspNetCore.TestHost
                     request.PathBase = _pathBase;
                 }
                 request.QueryString = QueryString.FromUriComponent(uri);
-                request.Headers.Add("Connection", new string[] { "Upgrade" });
-                request.Headers.Add("Upgrade", new string[] { "websocket" });
-                request.Headers.Add("Sec-WebSocket-Version", new string[] { "13" });
-                request.Headers.Add("Sec-WebSocket-Key", new string[] { CreateRequestKey() });
+                request.Headers.Add(HeaderNames.Connection, new string[] { "Upgrade" });
+                request.Headers.Add(HeaderNames.Upgrade, new string[] { "websocket" });
+                request.Headers.Add(HeaderNames.SecWebSocketVersion, new string[] { "13" });
+                request.Headers.Add(HeaderNames.SecWebSocketKey, new string[] { CreateRequestKey() });
+                if (SubProtocols.Any())
+                {
+                    request.Headers.Add(HeaderNames.SecWebSocketProtocol, SubProtocols.ToArray());
+                }
+
                 request.Body = Stream.Null;
 
                 // WebSocket
diff --git a/src/Hosting/TestHost/test/TestClientTests.cs b/src/Hosting/TestHost/test/TestClientTests.cs
index 322ab54a6f..aa1082b529 100644
--- a/src/Hosting/TestHost/test/TestClientTests.cs
+++ b/src/Hosting/TestHost/test/TestClientTests.cs
@@ -16,6 +16,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
+using Microsoft.Net.Http.Headers;
 using Xunit;
 
 namespace Microsoft.AspNetCore.TestHost
@@ -172,6 +173,7 @@ namespace Microsoft.AspNetCore.TestHost
             {
                 if (ctx.WebSockets.IsWebSocketRequest)
                 {
+                    Assert.False(ctx.Request.Headers.ContainsKey(HeaderNames.SecWebSocketProtocol));
                     var websocket = await ctx.WebSockets.AcceptWebSocketAsync();
                     var receiveArray = new byte[1024];
                     while (true)
@@ -232,6 +234,58 @@ namespace Microsoft.AspNetCore.TestHost
             clientSocket.Dispose();
         }
 
+        [Fact]
+        public async Task WebSocketSubProtocolsWorks()
+        {
+            // Arrange
+            RequestDelegate appDelegate = async ctx =>
+            {
+                if (ctx.WebSockets.IsWebSocketRequest)
+                {
+                    if (ctx.WebSockets.WebSocketRequestedProtocols.Contains("alpha") &&
+                        ctx.WebSockets.WebSocketRequestedProtocols.Contains("bravo"))
+                    {
+                        // according to rfc6455, the "server needs to include the same field and one of the selected subprotocol values"
+                        // however, this isn't enforced by either our server or client so it's possible to accept an arbitrary protocol.
+                        // Done here to demonstrate not "correct" behaviour, simply to show it's possible. Other clients may not allow this.
+                        var websocket = await ctx.WebSockets.AcceptWebSocketAsync("charlie");
+                        await websocket.CloseAsync(WebSocketCloseStatus.NormalClosure, "Normal Closure", CancellationToken.None);
+                    }
+                    else
+                    {
+                        var subprotocols = ctx.WebSockets.WebSocketRequestedProtocols.Any()
+                            ? string.Join(", ", ctx.WebSockets.WebSocketRequestedProtocols)
+                            : "<none>";
+                        var closeReason = "Unexpected subprotocols: " + subprotocols;
+                        var websocket = await ctx.WebSockets.AcceptWebSocketAsync();
+                        await websocket.CloseAsync(WebSocketCloseStatus.InternalServerError, closeReason, CancellationToken.None);
+                    }
+                }
+            };
+            var builder = new WebHostBuilder()
+                .Configure(app =>
+                {
+                    app.Run(appDelegate);
+                });
+            var server = new TestServer(builder);
+
+            // Act
+            var client = server.CreateWebSocketClient();
+            client.SubProtocols.Add("alpha");
+            client.SubProtocols.Add("bravo");
+            var clientSocket = await client.ConnectAsync(new Uri("wss://localhost"), CancellationToken.None);
+            var buffer = new byte[1024];
+            var result = await clientSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
+
+            // Assert
+            Assert.Equal(WebSocketMessageType.Close, result.MessageType);
+            Assert.Equal("Normal Closure", result.CloseStatusDescription);
+            Assert.Equal(WebSocketState.CloseReceived, clientSocket.State);
+            Assert.Equal("charlie", clientSocket.SubProtocol);
+
+            clientSocket.Dispose();
+        }
+
         [ConditionalFact]
         public async Task WebSocketAcceptThrowsWhenCancelled()
         {