diff --git a/src/Microsoft.AspNetCore.Server.HttpSys/FeatureContext.cs b/src/Microsoft.AspNetCore.Server.HttpSys/FeatureContext.cs
index f63599a..fd1dd9d 100644
--- a/src/Microsoft.AspNetCore.Server.HttpSys/FeatureContext.cs
+++ b/src/Microsoft.AspNetCore.Server.HttpSys/FeatureContext.cs
@@ -72,7 +72,7 @@ internal FeatureContext(RequestContext requestContext, bool enableResponseCachin
             _enableResponseCaching = enableResponseCaching;
 
             // Pre-initialize any fields that are not lazy at the lower level.
-            _requestHeaders = new HeaderDictionary(Request.Headers);
+            _requestHeaders = Request.Headers;
             _httpMethod = Request.Method;
             _path = Request.Path;
             _pathBase = Request.PathBase;
@@ -82,7 +82,7 @@ internal FeatureContext(RequestContext requestContext, bool enableResponseCachin
             _user = _requestContext.User;
 
             _responseStream = new ResponseStream(requestContext.Response.Body, OnStart);
-            _responseHeaders = new HeaderDictionary(Response.Headers);
+            _responseHeaders = Response.Headers;
         }
 
         internal IFeatureCollection Features => _features;
diff --git a/src/Microsoft.AspNetCore.Server.HttpSys/HeaderDictionary.cs b/src/Microsoft.AspNetCore.Server.HttpSys/HeaderDictionary.cs
deleted file mode 100644
index fdc00ee..0000000
--- a/src/Microsoft.AspNetCore.Server.HttpSys/HeaderDictionary.cs
+++ /dev/null
@@ -1,204 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using System.Collections;
-using System.Collections.Generic;
-using Microsoft.AspNetCore.Http;
-using Microsoft.Extensions.Primitives;
-
-namespace Microsoft.AspNetCore.Server.HttpSys
-{
-    /// <summary>
-    /// Represents a wrapper for RequestHeaders and ResponseHeaders.
-    /// </summary>
-    internal class HeaderDictionary : IHeaderDictionary
-    {
-        public HeaderDictionary(IDictionary<string, StringValues> store)
-        {
-            Store = store;
-        }
-
-        private IDictionary<string, StringValues> Store { get; set; }
-
-        /// <summary>
-        /// Get or sets the associated value from the collection as a single string.
-        /// </summary>
-        /// <param name="key">The header name.</param>
-        /// <returns>the associated value from the collection as a StringValues or StringValues.Empty if the key is not present.</returns>
-        public StringValues this[string key]
-        {
-            get
-            {
-                StringValues value;
-                if (TryGetValue(key, out value))
-                {
-                    return value;
-                }
-                return StringValues.Empty;
-            }
-            set
-            {
-                if (key == null)
-                {
-                    throw new ArgumentNullException(nameof(key));
-                }
-
-                if (StringValues.IsNullOrEmpty(value))
-                {
-                    Store.Remove(key);
-                }
-                else
-                {
-                    Store[key] = value;
-                }
-            }
-        }
-
-        /// <summary>
-        /// Throws KeyNotFoundException if the key is not present.
-        /// </summary>
-        /// <param name="key">The header name.</param>
-        /// <returns></returns>
-        StringValues IDictionary<string, StringValues>.this[string key]
-        {
-            get { return Store[key]; }
-            set { this[key] = value; }
-        }
-
-        /// <summary>
-        /// Gets the number of elements contained in the <see cref="T:HeaderDictionary" />;.
-        /// </summary>
-        /// <returns>The number of elements contained in the <see cref="T:HeaderDictionary" />.</returns>
-        public int Count
-        {
-            get { return Store.Count; }
-        }
-
-        /// <summary>
-        /// Gets a value that indicates whether the <see cref="T:HeaderDictionary" /> is in read-only mode.
-        /// </summary>
-        /// <returns>true if the <see cref="T:HeaderDictionary" /> is in read-only mode; otherwise, false.</returns>
-        public bool IsReadOnly
-        {
-            get { return Store.IsReadOnly; }
-        }
-
-        public ICollection<string> Keys
-        {
-            get { return Store.Keys; }
-        }
-
-        public ICollection<StringValues> Values
-        {
-            get { return Store.Values; }
-        }
-
-        /// <summary>
-        /// Adds a new list of items to the collection.
-        /// </summary>
-        /// <param name="item">The item to add.</param>
-        public void Add(KeyValuePair<string, StringValues> item)
-        {
-            Store.Add(item.Key, item.Value);
-        }
-
-        /// <summary>
-        /// Adds the given header and values to the collection.
-        /// </summary>
-        /// <param name="key">The header name.</param>
-        /// <param name="value">The header values.</param>
-        public void Add(string key, StringValues value)
-        {
-            Store.Add(key, value);
-        }
-
-        /// <summary>
-        /// Clears the entire list of objects.
-        /// </summary>
-        public void Clear()
-        {
-            Store.Clear();
-        }
-
-        /// <summary>
-        /// Returns a value indicating whether the specified object occurs within this collection.
-        /// </summary>
-        /// <param name="item">The item.</param>
-        /// <returns>true if the specified object occurs within this collection; otherwise, false.</returns>
-        public bool Contains(KeyValuePair<string, StringValues> item)
-        {
-            return Store.Contains(item);
-        }
-
-        /// <summary>
-        /// Determines whether the <see cref="T:HeaderDictionary" /> contains a specific key.
-        /// </summary>
-        /// <param name="key">The key.</param>
-        /// <returns>true if the <see cref="T:HeaderDictionary" /> contains a specific key; otherwise, false.</returns>
-        public bool ContainsKey(string key)
-        {
-            return Store.ContainsKey(key);
-        }
-
-        /// <summary>
-        /// Copies the <see cref="T:HeaderDictionary" /> elements to a one-dimensional Array instance at the specified index.
-        /// </summary>
-        /// <param name="array">The one-dimensional Array that is the destination of the specified objects copied from
-        /// the <see cref="T:HeaderDictionary" />.</param>
-        /// <param name="arrayIndex">The zero-based index in <paramref name="array" /> at which copying begins.</param>
-        public void CopyTo(KeyValuePair<string, StringValues>[] array, int arrayIndex)
-        {
-            Store.CopyTo(array, arrayIndex);
-        }
-
-        /// <summary>
-        /// Removes the given item from the the collection.
-        /// </summary>
-        /// <param name="item">The item.</param>
-        /// <returns>true if the specified object was removed from the collection; otherwise, false.</returns>
-        public bool Remove(KeyValuePair<string, StringValues> item)
-        {
-            return Store.Remove(item);
-        }
-
-        /// <summary>
-        /// Removes the given header from the collection.
-        /// </summary>
-        /// <param name="key">The header name.</param>
-        /// <returns>true if the specified object was removed from the collection; otherwise, false.</returns>
-        public bool Remove(string key)
-        {
-            return Store.Remove(key);
-        }
-
-        /// <summary>
-        /// Retrieves a value from the dictionary.
-        /// </summary>
-        /// <param name="key">The header name.</param>
-        /// <param name="value">The value.</param>
-        /// <returns>true if the <see cref="T:HeaderDictionary" /> contains the key; otherwise, false.</returns>
-        public bool TryGetValue(string key, out StringValues value)
-        {
-            return Store.TryGetValue(key, out value);
-        }
-
-        /// <summary>
-        /// Returns an enumerator that iterates through a collection.
-        /// </summary>
-        /// <returns>An <see cref="T:IEnumerator" /> object that can be used to iterate through the collection.</returns>
-        public IEnumerator GetEnumerator()
-        {
-            return Store.GetEnumerator();
-        }
-
-        /// <summary>
-        /// Returns an enumerator that iterates through a collection.
-        /// </summary>
-        /// <returns>An <see cref="T:IEnumerator" /> object that can be used to iterate through the collection.</returns>
-        IEnumerator<KeyValuePair<string, StringValues>> IEnumerable<KeyValuePair<string, StringValues>>.GetEnumerator()
-        {
-            return Store.GetEnumerator();
-        }
-    }
-}
diff --git a/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/HeaderCollection.cs b/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/HeaderCollection.cs
index 4f6cd22..1eef943 100644
--- a/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/HeaderCollection.cs
+++ b/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/HeaderCollection.cs
@@ -4,12 +4,17 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Primitives;
+using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNetCore.Server.HttpSys
 {
-    internal class HeaderCollection : IDictionary<string, StringValues>
+    internal class HeaderCollection : IHeaderDictionary
     {
+        private long? _contentLength;
+        private StringValues _contentLengthText;
+
         public HeaderCollection()
             : this(new Dictionary<string, StringValues>(4, StringComparer.OrdinalIgnoreCase))
         {
@@ -75,6 +80,52 @@ public ICollection<StringValues> Values
             get { return Store.Values; }
         }
 
+        public long? ContentLength
+        {
+            get
+            {
+                long value;
+                var rawValue = this[HttpKnownHeaderNames.ContentLength];
+
+                if (_contentLengthText.Equals(rawValue))
+                {
+                    return _contentLength;
+                }
+
+                if (rawValue.Count == 1 &&
+                    !string.IsNullOrWhiteSpace(rawValue[0]) &&
+                    HeaderUtilities.TryParseInt64(new StringSegment(rawValue[0]).Trim(), out value))
+                {
+                    _contentLengthText = rawValue;
+                    _contentLength = value;
+                    return value;
+                }
+
+                return null;
+            }
+            set
+            {
+                ThrowIfReadOnly();
+
+                if (value.HasValue)
+                {
+                    if (value.Value < 0)
+                    {
+                        throw new ArgumentOutOfRangeException("value", value.Value, "Cannot be negative.");
+                    }
+                    _contentLengthText = HeaderUtilities.FormatInt64(value.Value);
+                    this[HttpKnownHeaderNames.ContentLength] = _contentLengthText;
+                    _contentLength = value;
+                }
+                else
+                {
+                    Remove(HttpKnownHeaderNames.ContentLength);
+                    _contentLengthText = StringValues.Empty;
+                    _contentLength = null;
+                }
+            }
+        }
+
         public void Add(KeyValuePair<string, StringValues> item)
         {
             ThrowIfReadOnly();
diff --git a/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/Response.cs b/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/Response.cs
index d9f0958..31846b6 100644
--- a/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/Response.cs
+++ b/src/Microsoft.AspNetCore.Server.HttpSys/RequestProcessing/Response.cs
@@ -147,48 +147,8 @@ internal long ExpectedBodyLength
         // Header accessors
         public long? ContentLength
         {
-            get
-            {
-                string contentLengthString = Headers[HttpKnownHeaderNames.ContentLength];
-                long contentLength;
-                if (!string.IsNullOrWhiteSpace(contentLengthString))
-                {
-                    contentLengthString = contentLengthString.Trim();
-                    if (string.Equals(Constants.Zero, contentLengthString, StringComparison.Ordinal))
-                    {
-                        return 0;
-                    }
-                    else if (long.TryParse(contentLengthString, NumberStyles.None, CultureInfo.InvariantCulture.NumberFormat, out contentLength))
-                    {
-                        return contentLength;
-                    }
-                }
-                return null;
-            }
-            set
-            {
-                CheckResponseStarted();
-                if (!value.HasValue)
-                {
-                    Headers.Remove(HttpKnownHeaderNames.ContentLength);
-                }
-                else
-                {
-                    if (value.Value < 0)
-                    {
-                        throw new ArgumentOutOfRangeException("value", value.Value, "Cannot be negative.");
-                    }
-
-                    if (value.Value == 0)
-                    {
-                        Headers[HttpKnownHeaderNames.ContentLength] = Constants.Zero;
-                    }
-                    else
-                    {
-                        Headers[HttpKnownHeaderNames.ContentLength] = value.Value.ToString(CultureInfo.InvariantCulture);
-                    }
-                }
-            }
+            get { return Headers.ContentLength; }
+            set { Headers.ContentLength = value; }
         }
 
         /// <summary>
diff --git a/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/RequestTests.cs b/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/RequestTests.cs
index bb4688e..1e79dff 100644
--- a/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/RequestTests.cs
+++ b/test/Microsoft.AspNetCore.Server.HttpSys.FunctionalTests/RequestTests.cs
@@ -83,7 +83,7 @@ public async Task Request_FieldsCanBeSet_Set()
                     Assert.Equal("TEST", requestInfo.Method);
                     requestInfo.Body = new MemoryStream();
                     Assert.IsType<MemoryStream>(requestInfo.Body);
-                    var customHeaders = new HeaderDictionary(new HeaderCollection());
+                    var customHeaders = new HeaderCollection();
                     requestInfo.Headers = customHeaders;
                     Assert.Same(customHeaders, requestInfo.Headers);
                     requestInfo.Scheme = "abcd";