It’s typically around this time each holiday season that panic sets in for some buyers about whether gifts they have ordered will be delivered on time. Websites have started warning customers of the last day they should order to ensure their packages arrive before Christmas. But the surge in holiday shopping is slowing down the speed of deliveries, meaning you may need to wrap things up a little earlier this year.
UPS ups has already warned of delays. Now pilots that deliver for DHL and Amazon’s Prime Air amzn say they’re experiencing them too. (Amazon says it has not seen any Prime Air delays.)
FedEx fdx doesn’t seem to be experiencing widespread problems, according to ShipEx, which tracks deliveries (though some consumers have seen packages delayed by a day or two). As expected, volume at the delivery service is notably higher than usual.
More from FORTUNE
2017 has seen a surge in online shopping—with Cyber Monday setting records as consumers spent $6.59 billion, a nearly 17% increase over last year. That has taxed the infrastructure of shipping companies, particularly UPS, which handles shipping for Amazon, Walmart wmt , and other major retailers.
UPS told the Washington Post it expects to deliver 750 million packages this holiday season. FedEx will deliver 400 million.
To keep consumers happy (and, perhaps, garner a few more sales), many brick and mortar retailers are encouraging customers to ship items to their local stores. Since those items are handled by different contractors, they often don’t experience the same shipping delays.
(Editor’s note: This post has been updated to reflect comments from Amazon.)