A few years ago, when more people started searching through their phones and tablets than on desktop computers, Google changed its algorithm to give higher rankings to sites that display well on a mobile device.

Then, in late 2016, the company said it would start steering its ranking systems towards the mobile rather than desktop versions of sites. This was because desktop sites sometimes include elements that are missing on their mobile versions—if a mobile user clicks on a Google result expecting to see something that then doesn’t show up, it’s frustrating.

Now, after a year and a half of experimenting with that latter shift, Google said it has started steering its search algorithm towards the mobile versions of sites that “follow the best practices for mobile-first indexing.” That essentially means sites that include the same content and metadata on both mobile and desktop versions.

“Our crawling, indexing, and ranking systems have typically used the desktop version of a page’s content, which may cause issues for mobile searchers when that version is vastly different from the mobile version,” wrote software engineer Fan Zhang. “Mobile-first indexing means that we’ll use the mobile version of the page for indexing and ranking, to better help our—primarily mobile—users find what they’re looking for.”

Google stressed that those running sites with only desktop-friendly content needn’t panic, as “content gathered by mobile-first indexing has no ranking advantage over mobile content that’s not yet gathered this way or desktop content.”

However, it was clear that people should continue to make their sites more mobile-friendly, due to the ranking changes Google introduced in 2015.