Trying to buy an item, only to find that it’s out of stock, can be frustrating — especially when it’s something that you purchase regularly. Amazon and other stores realize this, so they provide an option to notify you when the item is back in stock. However, this won’t do you much good if you need to get the item right away. Maybe it sold out yesterday and won’t be restocked for months. In these cases, getting notified when the item is back in stock seems like too little, too late.

But there’s a variation that retailers could employ to make customers a lot happier. Instead of just telling people when something is back in stock, tell the regular buyers of that item when it’s almost sold out. In other words, when there’s only a few of the item left, send an email to anyone who buys the product frequently — and give them a chance to replenish their own supply before you run out.

With this approach, you’ll make your loyal customers happier, while also gleaning valuable data about how quickly you can sell the remaining stock when needed. This can reduce your risk in carrying additional inventory for those items, which should make it easier to avoid running out in the first place.