In a statement provided to Fortune, an Apple spokesperson said, “Today we launched a keyboard service program for our customers that covers a small percentage of keyboards in certain MacBook and MacBook Pro models which may exhibit one or more of the following behaviors: letters or characters that repeat unexpectedly or don’t appear when pressed or keys that feel ‘sticky’ or aren’t responding in a consistent manner.”

The laptop models affected rely on a new key switch design Apple introduced in 2015 with a complete revision of its MacBook laptop and brought to the MacBook Pro in an overhaul in 2016. The so-called “butterfly” keys allowed for a much lower-profile keyboard with reduced travel distance when pressed. Many users disliked the feel compared to standard “scissor” switch laptop keys. Beyond finger feel, the shorter travel distance also increased the likelihood that trapped grit—even small particles of dust—could lodge in place, preventing a key or keys from working.

The cost of out of warranty repair can be as high as $700, as keys can often not be repaired singly. Replacing the keyboard as a whole requires swapping out the entire top side of the main laptop body.

Apple currently faces three lawsuits over the keyboard flaw. Its offer to pay for repairs to the keyboard already performed may affect these suits, but no settlements were announced today.

It has been impossible to date to know how rare the problem is, as Apple doesn’t disclose rates of repair. In October 2017, technology journalist Casey Johnston wrote about her pervasive problem with a MacBook Pro’s keyboard, and said Apple repair technicians (known as Geniuses) repeatedly chalked it up to dust. Johnston spoke to an anonymous source at a company that provides MacBook Pros to its users, who said the problem was extensive but below 5% of laptops.

Apple posted special cleaning instructions for laptops with butterfly key switches in 2017, but no other information. Jason Snell, editor of Six Colors and former editor-in-chief of Macworld magazine, wrote in April 2018, “Apple’s relative silence on this issue for existing customers is deafening.” Snell called for a recall if the problem was pervasive as it seemed.

In April 2018, Johnston wrote a follow-up story that even after a replacement of her first keyboard, problems arose again, and she sold the laptop back Apple. She recommended against purchase of any butterfly-key models. (This reporter owns a 2015 MacBook with the butterfly design, which had its keyboard replaced in 2017 under a three-year paid warranty extension due to the key faces wearing off across all its most-used keys.)

Apple said affected customers can receive service at no charge via a retail Apple Store, through Apple’s mail-in repair program, or through an Apple-authorized service provider. If a laptop has other damage that has to be fixed before the keyboard can be replaced, Apple said in its service program page that a charge may apply.