diff --git a/src/Microsoft.AspNet.TestHost/ClientHandler.cs b/src/Microsoft.AspNet.TestHost/ClientHandler.cs
index a5f61bd4f9..df72462e24 100644
--- a/src/Microsoft.AspNet.TestHost/ClientHandler.cs
+++ b/src/Microsoft.AspNet.TestHost/ClientHandler.cs
@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
 using System.IO;
@@ -135,14 +136,14 @@ namespace Microsoft.AspNet.TestHost
 
                 foreach (var header in request.Headers)
                 {
-                    serverRequest.Headers.AppendValues(header.Key, header.Value.ToArray());
+                    serverRequest.Headers.Append(header.Key, header.Value.ToArray());
                 }
                 var requestContent = request.Content;
                 if (requestContent != null)
                 {
                     foreach (var header in request.Content.Headers)
                     {
-                        serverRequest.Headers.AppendValues(header.Key, header.Value.ToArray());
+                        serverRequest.Headers.Append(header.Key, header.Value.ToArray());
                     }
                 }
 
@@ -187,9 +188,9 @@ namespace Microsoft.AspNet.TestHost
 
                 foreach (var header in HttpContext.Response.Headers)
                 {
-                    if (!response.Headers.TryAddWithoutValidation(header.Key, header.Value))
+                    if (!response.Headers.TryAddWithoutValidation(header.Key, (IEnumerable<string>)header.Value))
                     {
-                        bool success = response.Content.Headers.TryAddWithoutValidation(header.Key, header.Value);
+                        bool success = response.Content.Headers.TryAddWithoutValidation(header.Key, (IEnumerable<string>)header.Value);
                         Contract.Assert(success, "Bad header");
                     }
                 }
diff --git a/src/Microsoft.AspNet.TestHost/RequestFeature.cs b/src/Microsoft.AspNet.TestHost/RequestFeature.cs
index eebdd28372..b55b02b6ff 100644
--- a/src/Microsoft.AspNet.TestHost/RequestFeature.cs
+++ b/src/Microsoft.AspNet.TestHost/RequestFeature.cs
@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using Microsoft.AspNet.Http.Features;
+using Microsoft.Framework.Primitives;
 
 namespace Microsoft.AspNet.TestHost
 {
@@ -13,7 +14,7 @@ namespace Microsoft.AspNet.TestHost
         public RequestFeature()
         {
             Body = Stream.Null;
-            Headers = new Dictionary<string, string[]>(StringComparer.OrdinalIgnoreCase);
+            Headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
             Method = "GET";
             Path = "";
             PathBase = "";
@@ -24,7 +25,7 @@ namespace Microsoft.AspNet.TestHost
 
         public Stream Body { get; set; }
 
-        public IDictionary<string, string[]> Headers { get; set; }
+        public IDictionary<string, StringValues> Headers { get; set; }
 
         public string Method { get; set; }
 
diff --git a/src/Microsoft.AspNet.TestHost/ResponseFeature.cs b/src/Microsoft.AspNet.TestHost/ResponseFeature.cs
index 25d9b3260d..2f699e572d 100644
--- a/src/Microsoft.AspNet.TestHost/ResponseFeature.cs
+++ b/src/Microsoft.AspNet.TestHost/ResponseFeature.cs
@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http.Features;
+using Microsoft.Framework.Primitives;
 
 namespace Microsoft.AspNet.TestHost
 {
@@ -16,7 +17,7 @@ namespace Microsoft.AspNet.TestHost
 
         public ResponseFeature()
         {
-            Headers = new Dictionary<string, string[]>(StringComparer.OrdinalIgnoreCase);
+            Headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
             Body = new MemoryStream();
 
             // 200 is the default status code all the way down to the host, so we set it
@@ -28,7 +29,7 @@ namespace Microsoft.AspNet.TestHost
 
         public string ReasonPhrase { get; set; }
 
-        public IDictionary<string, string[]> Headers { get; set; }
+        public IDictionary<string, StringValues> Headers { get; set; }
 
         public Stream Body { get; set; }