Monica Mazzei and Anne Freeman in “A Prenup Primer: What Silicon Valley Couples Should Consider” for the San Francisco Chronicle

Zynga co-founder Mark Pincus and his wife, Alison, had one. Snapchat CEO Evan Spiegel and actress Miranda Kerr reportedly have one. And in all likelihood, tennis star Serena Williams and Reddit co-founder Alexis Ohanian have one.

Increasingly, new world entrepreneurs who get married are turning to a practice more common in old-money ranks: prenuptial agreements meant to preserve one’s assets and pave the way for a smoother union — or make for a tidier breakup.

“Silicon Valley Millennial types are very aware of premarital agreements, very cognizant of protecting their million-dollar ideas and their stock options,” said Monica Mazzei, a family law attorney at Sideman & Bancroft in San Francisco, who has seen an uptick in requests in recent years for such legal documents, as well as for cohabitation agreements. “They might have a startup that might not have any ascertainable value now, but it could be a unicorn (worth $1 billion or more). They want to protect that.”