diff --git a/index.php b/index.php
index 1712a7d..a378266 100644
--- a/index.php
+++ b/index.php
@@ -218,6 +218,7 @@
 	{
 		if ( ! is_dir(BASEPATH.$application_folder.'/'))
 		{
+			header('HTTP/1.1 503 Service Unavailable.', TRUE, '503');
 			exit('Your application folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF);
 		}
 
@@ -233,6 +234,7 @@
 	{
 		if ( ! is_dir(APPPATH.'views/'))
 		{
+			header('HTTP/1.1 503 Service Unavailable.', TRUE, '503');
 			exit('Your view folder path does not appear to be set correctly. Please open the following file and correct this: '.SELF);
 		}
 
diff --git a/system/core/Common.php b/system/core/Common.php
index 2f9c4ff..225227d 100644
--- a/system/core/Common.php
+++ b/system/core/Common.php
@@ -177,6 +177,7 @@
 		{
 			// Note: We use exit() rather then show_error() in order to avoid a
 			// self-referencing loop with the Excptions class
+			set_status_header(503);
 			exit('Unable to locate the specified class: '.$class.'.php');
 		}
 
@@ -243,6 +244,7 @@
 		// Fetch the config file
 		if ( ! file_exists($file_path))
 		{
+			set_status_header(503);
 			exit('The configuration file does not exist.');
 		}
 
@@ -251,6 +253,7 @@
 		// Does the $config array exist in the file?
 		if ( ! isset($config) OR ! is_array($config))
 		{
+			set_status_header(503);
 			exit('Your config file does not appear to be formatted correctly.');
 		}
 
diff --git a/system/core/Input.php b/system/core/Input.php
index 7a16e51..ee15f40 100755
--- a/system/core/Input.php
+++ b/system/core/Input.php
@@ -25,8 +25,6 @@
  * @filesource
  */
 
-// ------------------------------------------------------------------------
-
 /**
  * Input Class
  *
@@ -152,7 +150,7 @@
 	public function get($index = NULL, $xss_clean = FALSE)
 	{
 		// Check if a field has been provided
-		if ($index === NULL AND ! empty($_GET))
+		if ($index === NULL && ! empty($_GET))
 		{
 			$get = array();
 
@@ -179,7 +177,7 @@
 	public function post($index = NULL, $xss_clean = FALSE)
 	{
 		// Check if a field has been provided
-		if ($index === NULL AND ! empty($_POST))
+		if ($index === NULL && ! empty($_POST))
 		{
 			$post = array();
 
@@ -206,9 +204,9 @@
 	*/
 	public function get_post($index = '', $xss_clean = FALSE)
 	{
-		return ( ! isset($_POST[$index]))
-			? $this->get($index, $xss_clean)
-			: $this->post($index, $xss_clean);
+		return isset($_POST[$index])
+			? $this->post($index, $xss_clean)
+			: $this->get($index, $xss_clean);
 	}
 
 	// --------------------------------------------------------------------
@@ -256,19 +254,19 @@
 			}
 		}
 
-		if ($prefix == '' AND config_item('cookie_prefix') != '')
+		if ($prefix == '' && config_item('cookie_prefix') != '')
 		{
 			$prefix = config_item('cookie_prefix');
 		}
-		if ($domain == '' AND config_item('cookie_domain') != '')
+		if ($domain == '' && config_item('cookie_domain') != '')
 		{
 			$domain = config_item('cookie_domain');
 		}
-		if ($path == '/' AND config_item('cookie_path') != '/')
+		if ($path == '/' && config_item('cookie_path') !== '/')
 		{
 			$path = config_item('cookie_path');
 		}
-		if ($secure == FALSE AND config_item('cookie_secure') != FALSE)
+		if ($secure == FALSE && config_item('cookie_secure') != FALSE)
 		{
 			$secure = config_item('cookie_secure');
 		}
@@ -320,11 +318,11 @@
 
 			$this->ip_address = in_array($_SERVER['REMOTE_ADDR'], $proxies) ? $_SERVER['HTTP_X_FORWARDED_FOR'] : $_SERVER['REMOTE_ADDR'];
 		}
-		elseif ( ! $this->server('HTTP_CLIENT_IP') AND $this->server('REMOTE_ADDR'))
+		elseif ( ! $this->server('HTTP_CLIENT_IP') && $this->server('REMOTE_ADDR'))
 		{
 			$this->ip_address = $_SERVER['REMOTE_ADDR'];
 		}
-		elseif ($this->server('REMOTE_ADDR') AND $this->server('HTTP_CLIENT_IP'))
+		elseif ($this->server('REMOTE_ADDR') && $this->server('HTTP_CLIENT_IP'))
 		{
 			$this->ip_address = $_SERVER['HTTP_CLIENT_IP'];
 		}
@@ -414,7 +412,7 @@
 			return $this->user_agent;
 		}
 
-		return $this->user_agent = ( ! isset($_SERVER['HTTP_USER_AGENT'])) ? FALSE : $_SERVER['HTTP_USER_AGENT'];
+		return $this->user_agent = isset($_SERVER['HTTP_USER_AGENT']) ? $_SERVER['HTTP_USER_AGENT'] : FALSE;
 	}
 
 	// --------------------------------------------------------------------
@@ -469,19 +467,16 @@
 		{
 			$_GET = array();
 		}
-		else
+		elseif (is_array($_GET) && count($_GET) > 0)
 		{
-			if (is_array($_GET) AND count($_GET) > 0)
+			foreach ($_GET as $key => $val)
 			{
-				foreach ($_GET as $key => $val)
-				{
-					$_GET[$this->_clean_input_keys($key)] = $this->_clean_input_data($val);
-				}
+				$_GET[$this->_clean_input_keys($key)] = $this->_clean_input_data($val);
 			}
 		}
 
 		// Clean $_POST Data
-		if (is_array($_POST) AND count($_POST) > 0)
+		if (is_array($_POST) && count($_POST) > 0)
 		{
 			foreach ($_POST as $key => $val)
 			{
@@ -490,7 +485,7 @@
 		}
 
 		// Clean $_COOKIE Data
-		if (is_array($_COOKIE) AND count($_COOKIE) > 0)
+		if (is_array($_COOKIE) && count($_COOKIE) > 0)
 		{
 			// Also get rid of specially treated cookies that might be set by a server
 			// or silly application, that are of no use to a CI application anyway
@@ -568,7 +563,7 @@
 		}
 
 		// Standardize newlines if needed
-		if ($this->_standardize_newlines == TRUE AND strpos($str, "\r") !== FALSE)
+		if ($this->_standardize_newlines == TRUE && strpos($str, "\r") !== FALSE)
 		{
 			return str_replace(array("\r\n", "\r", "\r\n\n"), PHP_EOL, $str);
 		}
@@ -592,6 +587,7 @@
 	{
 		if ( ! preg_match('/^[a-z0-9:_\/-]+$/i', $str))
 		{
+			set_status_header(503);
 			exit('Disallowed Key Characters.');
 		}
 
@@ -624,7 +620,7 @@
 		}
 		else
 		{
-			$headers['Content-Type'] = (isset($_SERVER['CONTENT_TYPE'])) ? $_SERVER['CONTENT_TYPE'] : @getenv('CONTENT_TYPE');
+			$headers['Content-Type'] = isset($_SERVER['CONTENT_TYPE']) ? $_SERVER['CONTENT_TYPE'] : @getenv('CONTENT_TYPE');
 
 			foreach ($_SERVER as $key => $val)
 			{
@@ -654,9 +650,9 @@
 	 *
 	 * Returns the value of a single member of the headers class member
 	 *
-	 * @param 	string		array key for $this->headers
-	 * @param	boolean		XSS Clean or not
-	 * @return 	mixed		FALSE on failure, string on success
+	 * @param	string	array key for $this->headers
+	 * @param	bool	XSS Clean or not
+	 * @return	mixed	FALSE on failure, string on success
 	 */
 	public function get_request_header($index, $xss_clean = FALSE)
 	{
@@ -670,12 +666,9 @@
 			return FALSE;
 		}
 
-		if ($xss_clean === TRUE)
-		{
-			return $this->security->xss_clean($this->headers[$index]);
-		}
-
-		return $this->headers[$index];
+		return ($xss_clean === TRUE)
+			? $this->security->xss_clean($this->headers[$index])
+			: $this->headers[$index];
 	}
 
 	// --------------------------------------------------------------------
@@ -685,11 +678,11 @@
 	 *
 	 * Test to see if a request contains the HTTP_X_REQUESTED_WITH header
 	 *
-	 * @return 	boolean
+	 * @return 	bool
 	 */
 	public function is_ajax_request()
 	{
-		return ($this->server('HTTP_X_REQUESTED_WITH') === 'XMLHttpRequest');
+		return ( ! empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) === 'xmlhttprequest');
 	}
 
 	// --------------------------------------------------------------------
@@ -699,11 +692,11 @@
 	 *
 	 * Test to see if a request was made from the command line
 	 *
-	 * @return 	boolean
+	 * @return 	bool
 	 */
 	public function is_cli_request()
 	{
-		return (php_sapi_name() === 'cli') or defined('STDIN');
+		return (php_sapi_name() === 'cli' OR defined('STDIN'));
 	}
 
 }
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 2e794a9..0b9d37e 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -102,6 +102,7 @@
 -  Fixed a bug (#904) - ``CI_Loader::initialize()`` caused a PHP Fatal error to be triggered if error level E_STRICT is used.
 -  Fixed a hosting edge case where an empty $_SERVER['HTTPS'] variable would evaluate to 'on'
 -  Fixed a bug (#154) - ``CI_Session::sess_update()`` caused the session to be destroyed on pages where multiple AJAX requests were executed at once.
+-  Fixed a possible bug in ``CI_Input::is_ajax_request()`` where some clients might not send the X-Requested-With HTTP header value exactly as 'XmlHttpRequest'.
 
 Version 2.1.0
 =============