Global advertising spend on social media is set to overtake newspapers in the next four years, according to a report released on Monday.

Social media advertising is growing at 20 percent a year and by 2019 will be worth $50.2 billion compared to $50.7 billion for newspapers, ad agency Zenith said in its “Advertising Expenditure Forecasts” study. But by 2020, the report adds, social media will be “comfortably” ahead.

Advertising on platforms like Facebook and Twitter will account for 20 percent of all internet advertising in 2019, up from 16 percent this year, according to the report.

“Social media platforms have benefited from the rapid adoption of mobile technology, using it to embed themselves into their users’ daily lives. For many users, social media is the focal point of their social lives as well as their main source of news. Social media ads blend seamlessly into the news feed, and are much more effective than interruptive banner formats, especially on mobile devices,” Zenith’s report said.

The uptick in social media spending is part of broader growth in the ad industry. Global advertising expenditure will grow 4.4 percent in 2017, matching the same pace seen in 2016, despite political uncertainties such as the U.S. presidential election and the U.K.’s referendum on European Union membership, according to the report.

Zenith forecasts ad spend to growth 4.4 percent in 2018 and 4.1 percent in 2019.

“Global adspend growth has been remarkably stable since 2010, growing at between 4 percent and 5 percent a year, generally at or below the growth rate of global GDP (gross domestic product). Before the financial crisis, advertising would typically exaggerate the wider economy, growing faster in times of expansion and shrinking faster during recessions, with frequent changes in year-on-year growth rates. More recently the global ad market appears to have entered a phase of more stable growth,” the report said.