diff --git a/lib/XMLHttpRequest.js b/lib/XMLHttpRequest.js
index 4b7cab4..8ea63e8 100644
--- a/lib/XMLHttpRequest.js
+++ b/lib/XMLHttpRequest.js
@@ -40,7 +40,8 @@ exports.XMLHttpRequest = function() {
     "Accept": "*/*",
   };
 
-  var headers = defaultHeaders;
+  var headers = {};
+  var headersCase = {};
 
   // These headers are not user setable.
   // The following are allowed but banned in the spec:
@@ -177,7 +178,7 @@ exports.XMLHttpRequest = function() {
   };
 
   /**
-   * Sets a header for the request.
+   * Sets a header for the request or appends the value if one is already set.
    *
    * @param string header Header name
    * @param string value Header value
@@ -193,7 +194,9 @@ exports.XMLHttpRequest = function() {
     if (sendFlag) {
       throw "INVALID_STATE_ERR: send flag is true";
     }
-    headers[header] = value;
+    header = headersCase[header.toLowerCase()] || header;
+    headersCase[header.toLowerCase()] = header;
+    headers[header] = headers[header] ? headers[header] + ', ' + value : value;
   };
 
   /**
@@ -243,9 +246,8 @@ exports.XMLHttpRequest = function() {
    * @return string Returns the request header or empty string if not set
    */
   this.getRequestHeader = function(name) {
-    // @TODO Make this case insensitive
-    if (typeof name === "string" && headers[name]) {
-      return headers[name];
+    if (typeof name === "string" && headersCase[name.toLowerCase()]) {
+      return headers[headersCase[name.toLowerCase()]];
     }
 
     return "";
@@ -325,6 +327,13 @@ exports.XMLHttpRequest = function() {
     // Add query string if one is used
     var uri = url.pathname + (url.search ? url.search : '');
 
+    // Set the defaults if they haven't been set
+    for (var name in defaultHeaders) {
+      if (!headersCase[name.toLowerCase()]) {
+        headers[name] = defaultHeaders[name];
+      }
+    }
+
     // Set the Host header or the server may reject the request
     headers["Host"] = host;
     if (!((ssl && port === 443) || port === 80)) {
diff --git a/tests/test-headers.js b/tests/test-headers.js
index 76454f1..23a419e 100644
--- a/tests/test-headers.js
+++ b/tests/test-headers.js
@@ -56,12 +56,16 @@ try {
   xhr.open("GET", "http://localhost:8000/");
   // Valid header
   xhr.setRequestHeader("X-Test", "Foobar");
+  xhr.setRequestHeader("X-Test2", "Foobar1");
+  xhr.setRequestHeader("X-Test2", "Foobar2");
   // Invalid header
   xhr.setRequestHeader("Content-Length", 0);
   // Allowed header outside of specs
   xhr.setRequestHeader("user-agent", "node-XMLHttpRequest-test");
   // Test getRequestHeader
   assert.equal("Foobar", xhr.getRequestHeader("X-Test"));
+  assert.equal("Foobar", xhr.getRequestHeader("x-tEST"));
+  assert.equal("Foobar1, Foobar2", xhr.getRequestHeader("x-test2"));
   // Test invalid header
   assert.equal("", xhr.getRequestHeader("Content-Length"));