In 2012, there were an estimated 200,000 people who spoke Finnish as their native language in Sweden, while 155,000 had Arabic.
But since then, many more Arabic speakers have come to Sweden as refugees, while the number of native Finnish speakers is declining.
"Most speakers of Finnish are also immigrants. But they came several decades ago and are now dying," the study's author Mikael Parkvall, a linguist at Stockholm University, tells Radio Sweden. "They have to some extent passed the language on to their children but not to the extent that it would compensate for their own deaths."
But conclusions about the number of people using a certain language in Sweden are not completely straightforward. Parkvall's own assessment is based on many different sources, ranging from official school and immigration data, as well as surveys and comparisons with other countries.
Unlike other countries, Sweden does not gather any official language statistics, since it's seen as too close to ethnic registration. This lack of official data is something Parkvall finds unfortunate.
"Tons of democracies actually do know which languages are spoken within their borders," he adds.