Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 15506)
+++ wp-includes/functions.php	(working copy)
@@ -85,8 +85,8 @@
 function date_i18n( $dateformatstring, $unixtimestamp = false, $gmt = false ) {
 	global $wp_locale;
 	$i = $unixtimestamp;
-	// Sanity check for PHP 5.1.0-
-	if ( false === $i || intval($i) < 0 ) {
+	// Sanity check for PHP 5.1.0- and for 32-bit systems.
+	if ( false === $i || ( intval($i) < 0 && ( -1 === strtotime( '1969-01-01' ) || $i != date( 'U', $i ) ) ) ) {
 		if ( ! $gmt )
 			$i = current_time( 'timestamp' );
 		else