It's hard to spend a lot of money at McDonald's, so you may not think to ask for a receipt when placing an order there. But even if you only paid a few dollars for your Big Mac and apple pie, you should still ask for proof of your purchase—if only to throw the slip in the trash a few seconds later. As Reader's Digest reports, simply asking for a receipt can improve the quality of your fast food meal.

A former UK McDonald's employee revealed this secret for getting the freshest food possible in a Quora post. Secret shoppers—or “gapbusters”—are paid to visit McDonald's restaurants to keep tabs on the service and quality. Workers aren't supposed to know which customers were sent by the company, but they've learned to look for clues. Gapbusters usually show up at prime mealtimes—between 12 and 2 p.m. or 5 to 7 p.m.—and they tend to ask for a receipt so they can be reimbursed for their order.

Many customers aren't too concerned about getting receipts for small purchases, so the request may immediately set employees on alert. If they assume the diner is a secret shopper, they may do everything possible to ensure their food is especially fresh and high-quality.

This tip comes from one former employee, and it may not apply to every McDonald's location in every part of the world. But if you want to avoid getting stale fries, asking for a paper receipt on your next visit couldn't hurt. The receipt trick is one of many unofficial McDonald's hacks that have become common knowledge on the internet. Another way to upgrade your meal is to ask for a refill of fries: Some customers have reported getting their empty cartons filled up for free. Here are more insider secrets from McDonald's employees.

[h/t Reader's Digest]