Index: class-wp-ajax-response.php
===================================================================
--- class-wp-ajax-response.php	(revision 19547)
+++ class-wp-ajax-response.php	(working copy)
@@ -126,11 +126,16 @@
 	 * @since 2.1.0
 	 */
 	function send() {
-		header('Content-Type: text/xml');
-		echo "<?xml version='1.0' standalone='yes'?><wp_ajax>";
+		$xml = "<?xml version='1.0' encoding='" . get_option('blog_charset') . "' standalone='yes'?><wp_ajax>";
 		foreach ( (array) $this->responses as $response )
-			echo $response;
-		echo '</wp_ajax>';
+			$xml .= $response;
+		$xml .= '</wp_ajax>';
+		$length = strlen($xml);
+
+		header('Content-Type: text/xml; charset=' . get_option('blog_charset'));
+		header('Content-Length: '.$length);
+
+		echo $xml;
 		die();
 	}
 }