diff --git a/nodejs/s3/s3handler.js b/nodejs/s3/s3handler.js
index 19435ec..92da09e 100644
--- a/nodejs/s3/s3handler.js
+++ b/nodejs/s3/s3handler.js
@@ -36,6 +36,7 @@ var express = require("express"),
 
 // Set these two values to match your environment
     expectedBucket = "fineuploadertest",
+    expectedHostname = "fineuploadertest.s3.amazonaws.com",
 
 // CHANGE TO INTEGERS TO ENABLE POLICY DOCUMENT VERIFICATION ON FILE SIZE
 // (recommended)
@@ -96,8 +97,9 @@ function signRequest(req, res) {
 
 // Signs multipart (chunked) requests.  Omit if you don't want to support chunking.
 function signRestRequest(req, res) {
-    var stringToSign = req.body.headers,
-        signature = req.query.v4 ? signV4RestRequest(stringToSign) : signV2RestRequest(stringToSign);
+    var version = req.query.v4 ? 4 : 2,
+        stringToSign = req.body.headers,
+        signature = version === 4 ? signV4RestRequest(stringToSign) : signV2RestRequest(stringToSign);
 
     var jsonResponse = {
         signature: signature
@@ -105,7 +107,7 @@ function signRestRequest(req, res) {
 
     res.setHeader("Content-Type", "application/json");
 
-    if (req.query.v4 || isValidRestRequest(stringToSign)) {
+    if (isValidRestRequest(stringToSign, version)) {
         res.end(JSON.stringify(jsonResponse));
     }
     else {
@@ -119,8 +121,11 @@ function signV2RestRequest(headersStr) {
 }
 
 function signV4RestRequest(headersStr) {
-    var matches = /.+\n.+\n(\d+)\/(.+)\/s3\/.+\n(.+)/.exec(headersStr);
-    return getV4SignatureKey(clientSecretKey, matches[1], matches[2], "s3", headersStr);
+    var matches = /.+\n.+\n(\d+)\/(.+)\/s3\/aws4_request\n([\s\S]+)/.exec(headersStr),
+        hashedCanonicalRequest = CryptoJS.SHA256(matches[3]),
+        stringToSign = headersStr.replace(/(.+s3\/aws4_request\n)[\s\S]+/, '$1' + hashedCanonicalRequest);
+
+    return getV4SignatureKey(clientSecretKey, matches[1], matches[2], "s3", stringToSign);
 }
 
 // Signs "simple" (non-chunked) upload requests.
@@ -166,7 +171,11 @@ function signV4Policy(policy, base64Policy) {
 
 // Ensures the REST request is targeting the correct bucket.
 // Omit if you don't want to support chunking.
-function isValidRestRequest(headerStr) {
+function isValidRestRequest(headerStr, version) {
+    if (version === 4) {
+        return new RegExp("host:" + expectedHostname).exec(headerStr) != null;
+    }
+
     return new RegExp("\/" + expectedBucket + "\/.+$").exec(headerStr) != null;
 }