Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 35460)
+++ wp-includes/functions.php	(working copy)
@@ -261,7 +261,7 @@
 	$start = $day - DAY_IN_SECONDS * ( $weekday - $start_of_week );
 
 	// $start + 7 days - 1 second.
-	$end = $start + 7 * DAY_IN_SECONDS - 1;
+	$end = $start + WEEK_IN_SECONDS - 1;
 	return compact( 'start', 'end' );
 }