Online shoppers got Amazon's Echo Dot speaker for free on Friday.

Amazon (AMZN) listed the small smart speaker at $49.99 on its website, but customers received a $49.99 credit automatically that dropped the price down to $0 at checkout. The deal was removed shortly before 1 p.m. Pacific Time on Friday.

Customers received the $49.99 credit as an "Audible promo code."

It's unclear if the price drop was due to a special promotion or a technical glitch on Amazon.

Amazon's Echo speaker puts the Alexa smart assistant inside your home. The smart speakers can tell you the weather and traffic, read the news, and let you control a number of other apps with voice commands.

Amazon did not immediately respond to a request for comment.