如何使用Carbon获取过去特定月份的最后一次出现？

I'm looking for a simple, neat way to get a timestamp with Carbon of the last occurance of a specific month in the past. Currently I'm doing it like so, but I think that has to be a more fluent way:

if(date('m') >= 8) {
   $lastAugust = new Carbon('first day of august');
} else {
   $lastAugust = new Carbon('first day of august last year');
}

Anyone ideas?