That ironic twist for the world’s biggest online retailer was reported on Tuesday by the Wall Street Journal, which said the top-selling speakers that create a connected home, can still be found at Amazon’s brick-and-mortar stores. Online customers have to wait until after Christmas to receive their orders.

“Due to demand, we encourage customers to purchase an Echo if they see it available,” an Amazon spokeswoman told the Journal. An Amazon spokesperson was not immediately available to comment to Fortune.

The Echo and the smaller Echo Dot connect to Amazon’s interactive, connected-home system called Alexa, introduced in late 2014. The system responds to voice commands, which allow users to create lists, search the web, check weather conditions, or play podcasts, among other things.

The Dot, released earlier this year, was Amazon’s best-selling online item following the Thanksgiving holiday, with sales likely goosed by a 20% discount that brought the price down to $39.99. The Echo and Echo Dot normally retail for $179 and $49.99 respectively.

There’s a lesson here for businesses much smaller than Amazon: You need to be diligent about your supply chain, particularly during the holidays.

“This is why it is so important for small-business owners to stay close to their customers, maintain strong relationships with suppliers, follow market trends, and really know their industry,” says Bruce Bachenheimer, a clinical professor of management at Pace University in New York. “They cannot simply rely on the recommendations of a sales rep and act as stock keepers or inventory managers.”

Related: How to Buy the Amazon Echo Dot and Other Sold-Out Amazon Devices

Amazon distributes items from 146 warehouses worldwide, the Journal reports. It sells the Echo devices from three bricks and mortar bookstores in Boston, San Diego, and Seattle, as well as from 30 pop-up locations at malls. Amazon plans to open convenience stores for its Amazon Fresh grocery service in the coming months.

The Echo has sold more than 5 million units since the launch of Alexa, according to industry reports.