Problem with strtotime() and 2002-03-31

I have used the following script successfully for a year now, but have just found a problem with the date 2002-03-31. When I add 0 days to this date it returns 2002-03-31. Correct! When I add 1 day to this date it still returns 2002-03-31. NOT Correct n I add 2 days to this date it returns 2002-03-31. NOT correct So far this is the only date that I havefound a problem with. Any ideas why this would be happening? function addDays($date,$nofdays) { $dd=strtotime($date); $dd2=$dd + (3600*24*$nofdays); return date("Y-m-d", $dd2); } $nd=addDays("2002-03-31","2"); echo $nd Regards John Clarke