Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 21293)
+++ wp-includes/formatting.php	(working copy)
@@ -1,4 +1,4 @@
-<?php
+?<?php
 /**
  * Main WordPress Formatting API.
  *
@@ -1868,11 +1868,11 @@
 	$tz = get_option('timezone_string');
 	if ( $tz ) {
 		date_default_timezone_set( $tz );
-		$datetime = new DateTime( $string );
-		$datetime->setTimezone( new DateTimeZone('UTC') );
-		$offset = $datetime->getOffset();
-		$datetime->modify( '+' . $offset / 3600 . ' hours');
-		$string_gmt = gmdate($format, $datetime->format('U'));
+		$datetimeObj = date_create( $string );
+		$datetimeObj = date_timezone_set( $datetimeObj, timezone_open('UTC') );
+		$offset = date_offset_get($datetimeObj);
+		$datetimeObj = date_modify( $datetimeObj, ($offset < 0 ? '-':'+') . abs($offset / 3600) . ' hours');
+		$string_gmt = gmdate( $format, date_format($datetimeObj, 'U') );
 
 		date_default_timezone_set('UTC');
 	} else {