diff --git a/lib/Cake/Test/Case/View/Helper/JsHelperTest.php b/lib/Cake/Test/Case/View/Helper/JsHelperTest.php
index 92d1038db..e1c1e5fd2 100644
--- a/lib/Cake/Test/Case/View/Helper/JsHelperTest.php
+++ b/lib/Cake/Test/Case/View/Helper/JsHelperTest.php
@@ -302,10 +302,20 @@ class JsHelperTest extends CakeTestCase {
  */
 	public function testWriteBufferAndXhr() {
 		$this->_useMock();
-		$this->Js->params['isAjax'] = true;
+		$requestWith = null;
+		if (isset($_SERVER['HTTP_X_REQUESTED_WITH'])) {
+			$requestWith = $_SERVER['HTTP_X_REQUESTED_WITH'];
+		}
+		$_SERVER['HTTP_X_REQUESTED_WITH'] = 'XMLHttpRequest';
+
 		$this->Js->buffer('alert("test");');
 		$this->Js->TestJsEngine->expects($this->never())->method('domReady');
 		$result = $this->Js->writeBuffer();
+
+		unset($_SERVER['HTTP_X_REQUESTED_WITH']);
+		if ($requestWith !== null) {
+			$_SERVER['HTTP_X_REQUESTED_WITH'] = $requestWith;
+		}
 	}
 
 /**
diff --git a/lib/Cake/View/Helper/JsHelper.php b/lib/Cake/View/Helper/JsHelper.php
index 92c3e3bee..c62efe75d 100644
--- a/lib/Cake/View/Helper/JsHelper.php
+++ b/lib/Cake/View/Helper/JsHelper.php
@@ -190,7 +190,7 @@ class JsHelper extends AppHelper {
  * @link http://book.cakephp.org/2.0/en/core-libraries/helpers/js.html#JsHelper::writeBuffer
  */
 	public function writeBuffer($options = array()) {
-		$domReady = $this->request->is('ajax');
+		$domReady = !$this->request->is('ajax');
 		$defaults = array(
 			'onDomReady' => $domReady, 'inline' => true,
 			'cache' => false, 'clear' => true, 'safe' => true