Microsoft founder Bill Gates delivered a strong message to Europe during a recent interview with a German news outlet: Control your borders.

Gates, who donated to the Obama campaign, warned during an interview with Welt am Sonntag — first translated by Breitbart News — that Germany’s open border policies will likely lead to a national catastrophe.

Gates believes that the nation’s foremost dilemma derives from its “attitude towards refugees.”

The tech entrepreneur’s criticism took specific aim at German chancellor Angela Merkel, who has been a strong advocate for taking in tens of thousands of migrants.

“Germany cannot possibly take in the huge, massive number of people who are wanting to make their way to Europe” Gates asserted, referring to the over one million migrants Germany welcomed in 2015.

Gates goes on to suggest that Europe as a whole needs to make it “more difficult for Africans to reach the continent via the current transit routes.”

As an alternative to mass migration, the tech titan suggests Europe spend more on foreign aid to cut incentive to relocate. “The more generous you are, the more word gets around about this – which in turn motivates more people to leave Africa,” Gates said in the interview.