diff --git a/Sources/NIOHTTP1/HTTPTypes.swift b/Sources/NIOHTTP1/HTTPTypes.swift
index 594d5bd564..9388ec109e 100644
--- a/Sources/NIOHTTP1/HTTPTypes.swift
+++ b/Sources/NIOHTTP1/HTTPTypes.swift
@@ -19,27 +19,76 @@ let headerSeparator: StaticString = ": "
 
 /// A representation of the request line and header fields of a HTTP request.
 public struct HTTPRequestHead: Equatable {
+    private final class _Storage {
+        var method: HTTPMethod
+        var rawURI: URI
+        var version: HTTPVersion
+
+        init(method: HTTPMethod, rawURI: URI, version: HTTPVersion) {
+            self.method = method
+            self.rawURI = rawURI
+            self.version = version
+        }
+
+        func copy() -> _Storage {
+            return .init(method: self.method, rawURI: self.rawURI, version: self.version)
+        }
+    }
+
+    private var _storage: _Storage
+
+    /// The header fields for this HTTP request.
+    // warning: do not put this in `_Storage` as it'd trigger a CoW on every mutation
+    public var headers: HTTPHeaders
+
     /// The HTTP method for this request.
-    public var method: HTTPMethod
+    public var method: HTTPMethod {
+        get {
+            return self._storage.method
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = self._storage.copy()
+            }
+            self._storage.method = newValue
+        }
+    }
 
     // Internal representation of the URI.
-    private var rawURI: URI
+    private var rawURI: URI {
+        get {
+            return self._storage.rawURI
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = self._storage.copy()
+            }
+            self._storage.rawURI = newValue
+        }
+    }
 
     /// The URI used on this request.
     public var uri: String {
-        get { 
-            return String(uri: rawURI) 
+        get {
+            return String(uri: rawURI)
         }
-        set { 
+        set {
             rawURI = .string(newValue) 
         }
     }
 
     /// The version for this HTTP request.
-    public var version: HTTPVersion
-
-    /// The header fields for this HTTP request.
-    public var headers: HTTPHeaders
+    public var version: HTTPVersion {
+        get {
+            return self._storage.version
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = self._storage.copy()
+            }
+            self._storage.version = newValue
+        }
+    }
 
     /// Create a `HTTPRequestHead`
     ///
@@ -57,10 +106,8 @@ public struct HTTPRequestHead: Equatable {
     /// - Parameter rawURI: The URI used on this request.
     /// - Parameter headers: The headers for this HTTP request.
     init(version: HTTPVersion, method: HTTPMethod, rawURI: URI, headers: HTTPHeaders) {
-        self.version = version
-        self.method = method
-        self.rawURI = rawURI
         self.headers = headers
+        self._storage = _Storage(method: method, rawURI: rawURI, version: version)
     }
 
     public static func ==(lhs: HTTPRequestHead, rhs: HTTPRequestHead) -> Bool {
@@ -142,24 +189,58 @@ extension HTTPRequestHead {
 
 /// A representation of the status line and header fields of a HTTP response.
 public struct HTTPResponseHead: Equatable {
-    /// The HTTP response status.
-    public var status: HTTPResponseStatus
+    private final class _Storage {
+        var status: HTTPResponseStatus
+        var version: HTTPVersion
+        init(status: HTTPResponseStatus, version: HTTPVersion) {
+            self.status = status
+            self.version = version
+        }
+        func copy() -> _Storage {
+            return .init(status: self.status, version: self.version)
+        }
+    }
 
-    /// The HTTP version that corresponds to this response.
-    public var version: HTTPVersion
+    private var _storage: _Storage
 
     /// The HTTP headers on this response.
+    // warning: do not put this in `_Storage` as it'd trigger a CoW on every mutation
     public var headers: HTTPHeaders
 
+    /// The HTTP response status.
+    public var status: HTTPResponseStatus {
+        get {
+            return self._storage.status
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = self._storage.copy()
+            }
+            self._storage.status = newValue
+        }
+    }
+
+    /// The HTTP version that corresponds to this response.
+    public var version: HTTPVersion {
+        get {
+            return self._storage.version
+        }
+        set {
+            if !isKnownUniquelyReferenced(&self._storage) {
+                self._storage = self._storage.copy()
+            }
+            self._storage.version = newValue
+        }
+    }
+
     /// Create a `HTTPResponseHead`
     ///
     /// - Parameter version: The version for this HTTP response.
     /// - Parameter status: The status for this HTTP response.
     /// - Parameter headers: The headers for this HTTP response.
     public init(version: HTTPVersion, status: HTTPResponseStatus, headers: HTTPHeaders = HTTPHeaders()) {
-        self.version = version
-        self.status = status
         self.headers = headers
+        self._storage = _Storage(status: status, version: version)
     }
 
     public static func ==(lhs: HTTPResponseHead, rhs: HTTPResponseHead) -> Bool {
@@ -220,10 +301,35 @@ private extension UInt8 {
 /// can be represented appropriately.
 public struct HTTPHeaders: CustomStringConvertible {
 
+    private final class _Storage {
+        var buffer: ByteBuffer
+        var headers: [HTTPHeader]
+        var continuous: Bool = true
+
+        init(buffer: ByteBuffer, headers: [HTTPHeader], continuous: Bool) {
+            self.buffer = buffer
+            self.headers = headers
+            self.continuous = continuous
+        }
+
+        func copy() -> _Storage {
+            return .init(buffer: self.buffer, headers: self.headers, continuous: self.continuous)
+        }
+    }
+    private var _storage: _Storage
+
     // Because we use CoW implementations HTTPHeaders is also CoW
-    fileprivate var buffer: ByteBuffer
-    fileprivate var headers: [HTTPHeader]
-    fileprivate var continuous: Bool = true
+    fileprivate var buffer: ByteBuffer {
+        return self._storage.buffer
+    }
+
+    fileprivate var headers: [HTTPHeader] {
+        return self._storage.headers
+    }
+
+    fileprivate var continuous: Bool {
+        return self._storage.continuous
+    }
 
     /// Returns the `String` for the given `HTTPHeaderIndex`.
     ///
@@ -251,8 +357,7 @@ public struct HTTPHeaders: CustomStringConvertible {
 
     /// Constructor used by our decoder to construct headers without the need of converting bytes to string.
     init(buffer: ByteBuffer, headers: [HTTPHeader]) {
-        self.buffer = buffer
-        self.headers = headers
+        self._storage = _Storage(buffer: buffer, headers: headers, continuous: true)
     }
 
     /// Construct a `HTTPHeaders` structure.
@@ -295,13 +400,16 @@ public struct HTTPHeaders: CustomStringConvertible {
     /// - Parameter value: The header field value to add for the given name.
     public mutating func add(name: String, value: String) {
         precondition(!name.utf8.contains(where: { !$0.isASCII }), "name must be ASCII")
+        if !isKnownUniquelyReferenced(&self._storage) {
+            self._storage = self._storage.copy()
+        }
         let nameStart = self.buffer.writerIndex
-        let nameLength = self.buffer.write(string: name)!
-        self.buffer.write(staticString: headerSeparator)
+        let nameLength = self._storage.buffer.write(string: name)!
+        self._storage.buffer.write(staticString: headerSeparator)
         let valueStart = self.buffer.writerIndex
-        let valueLength = self.buffer.write(string: value)!
-        self.headers.append(HTTPHeader(name: HTTPHeaderIndex(start: nameStart, length: nameLength), value: HTTPHeaderIndex(start: valueStart, length: valueLength)))
-        self.buffer.write(staticString: crlf)
+        let valueLength = self._storage.buffer.write(string: value)!
+        self._storage.headers.append(HTTPHeader(name: HTTPHeaderIndex(start: nameStart, length: nameLength), value: HTTPHeaderIndex(start: valueStart, length: valueLength)))
+        self._storage.buffer.write(staticString: crlf)
     }
 
     /// Add a header name/value pair to the block, replacing any previous values for the
@@ -346,10 +454,14 @@ public struct HTTPHeaders: CustomStringConvertible {
             return
         }
 
+        if !isKnownUniquelyReferenced(&self._storage) {
+            self._storage = self._storage.copy()
+        }
+
         array.forEach {
-            self.headers.remove(at: $0)
+            self._storage.headers.remove(at: $0)
         }
-        self.continuous = false
+        self._storage.continuous = false
     }
 
     /// Retrieve all of the values for a give header field name from the block.
diff --git a/Tests/NIOHTTP1Tests/HTTPTest+XCTest.swift b/Tests/NIOHTTP1Tests/HTTPTest+XCTest.swift
index b4d8ac9761..03471251a4 100644
--- a/Tests/NIOHTTP1Tests/HTTPTest+XCTest.swift
+++ b/Tests/NIOHTTP1Tests/HTTPTest+XCTest.swift
@@ -34,6 +34,8 @@ extension HTTPTest {
                 ("test1ByteHTTPBody", test1ByteHTTPBody),
                 ("testHTTPPipeliningWithBody", testHTTPPipeliningWithBody),
                 ("testChunkedBody", testChunkedBody),
+                ("testHTTPRequestHeadCoWWorks", testHTTPRequestHeadCoWWorks),
+                ("testHTTPResponseHeadCoWWorks", testHTTPResponseHeadCoWWorks),
            ]
    }
 }
diff --git a/Tests/NIOHTTP1Tests/HTTPTest.swift b/Tests/NIOHTTP1Tests/HTTPTest.swift
index 952223ddde..86aebb45a2 100644
--- a/Tests/NIOHTTP1Tests/HTTPTest.swift
+++ b/Tests/NIOHTTP1Tests/HTTPTest.swift
@@ -206,4 +206,62 @@ class HTTPTest: XCTestCase {
         trailers.add(name: "Something", value: "Else")
         try checkHTTPRequest(HTTPRequestHead(version: HTTPVersion(major: 1, minor: 1), method: .POST, uri: "/"), body: "100", trailers: trailers)
     }
+
+    func testHTTPRequestHeadCoWWorks() throws {
+        let headers = HTTPHeaders([("foo", "bar")])
+        var httpReq = HTTPRequestHead(version: HTTPVersion(major: 1, minor: 1), method: .GET, uri: "/uri")
+        httpReq.headers = headers
+
+        var modVersion = httpReq
+        modVersion.version = HTTPVersion(major: 2, minor: 0)
+        XCTAssertEqual(HTTPVersion(major: 1, minor: 1), httpReq.version)
+        XCTAssertEqual(HTTPVersion(major: 2, minor: 0), modVersion.version)
+
+        var modMethod = httpReq
+        modMethod.method = .POST
+        XCTAssertEqual(.GET, httpReq.method)
+        XCTAssertEqual(.POST, modMethod.method)
+
+        var modURI = httpReq
+        modURI.uri = "/changed"
+        XCTAssertEqual("/uri", httpReq.uri)
+        XCTAssertEqual("/changed", modURI.uri)
+
+        var modHeaders = httpReq
+        modHeaders.headers.add(name: "qux", value: "quux")
+        XCTAssertEqual(httpReq.headers, headers)
+        XCTAssertNotEqual(httpReq, modHeaders)
+        modHeaders.headers.remove(name: "foo")
+        XCTAssertEqual(httpReq.headers, headers)
+        XCTAssertNotEqual(httpReq, modHeaders)
+        modHeaders.headers.remove(name: "qux")
+        modHeaders.headers.add(name: "foo", value: "bar")
+        XCTAssertEqual(httpReq, modHeaders)
+    }
+
+    func testHTTPResponseHeadCoWWorks() throws {
+        let headers = HTTPHeaders([("foo", "bar")])
+        let httpRes = HTTPResponseHead(version: HTTPVersion(major: 1, minor: 1), status: .ok, headers: headers)
+
+        var modVersion = httpRes
+        modVersion.version = HTTPVersion(major: 2, minor: 0)
+        XCTAssertEqual(HTTPVersion(major: 1, minor: 1), httpRes.version)
+        XCTAssertEqual(HTTPVersion(major: 2, minor: 0), modVersion.version)
+
+        var modStatus = httpRes
+        modStatus.status = .notFound
+        XCTAssertEqual(.ok, httpRes.status)
+        XCTAssertEqual(.notFound, modStatus.status)
+
+        var modHeaders = httpRes
+        modHeaders.headers.add(name: "qux", value: "quux")
+        XCTAssertEqual(httpRes.headers, headers)
+        XCTAssertNotEqual(httpRes, modHeaders)
+        modHeaders.headers.remove(name: "foo")
+        XCTAssertEqual(httpRes.headers, headers)
+        XCTAssertNotEqual(httpRes, modHeaders)
+        modHeaders.headers.remove(name: "qux")
+        modHeaders.headers.add(name: "foo", value: "bar")
+        XCTAssertEqual(httpRes, modHeaders)
+    }
 }