Facebook has been prevented from making use of UK citizens' WhatsApp data for purposes beyond the chat app itself.
The firm had announced in 2016 that it intended to tap into its subsidiary's records to give better friend suggestions and show more relevant ads.
However, the UK's information commissioner said this would have breached existing data protection laws.
The US firm has now promised not to access the information until it becomes compliant with a new set of rules.
This is a reference to the forthcoming General Data Protection Regulation (GDPR), which comes into force on 25 May.
The legislation introduces new rules, including giving individuals the right to know the information an organisation holds about them - including data obtained from others.
At present, Facebook refuses to share so-called "shadow profile" information it has gathered about people via their friends and acquaintances.
It told the Gizmodo news site last year that it thought this would amount to a privacy violation of those who had provided the data.
Since then, the firm has given a commitment to make changes to obey the new rules.
The information commissioner, Elizabeth Denham, noted that a German court had confirmed the country's own data-sharing ban with regard to WhatsApp and Facebook earlier this month.
In addition, she highlighted that the ICO's French equivalent was also in the process of bringing its own enforcement action against the company.
"I would like to stress that signing an undertaking is not the end of the story," she added.
"I will closely monitor WhatsApp's adherence to it,"