Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 18502)
+++ wp-includes/functions.php	(working copy)
@@ -152,7 +152,7 @@
  */
 function number_format_i18n( $number, $decimals = 0 ) {
 	global $wp_locale;
-	$formatted = number_format( $number, absint( $decimals ), $wp_locale->number_format['decimal_point'], $wp_locale->number_format['thousands_sep'] );
+	$formatted = number_format( (float) $number, absint( $decimals ), $wp_locale->number_format['decimal_point'], $wp_locale->number_format['thousands_sep'] );
 	return apply_filters( 'number_format_i18n', $formatted );
 }