Melinda Gates says gender inequality in the U.S. “keeps me up at night.”

The billionaire and Bill & Melinda Gates Foundation cochair said in a Times op-ed that “a window of opportunity” for women has been “painstakingly pried open,” but she warned “there is no reason to believe this moment will last forever.” Gates used the op-ed to announce she’s spending $1 billion through her investment arm, Pivotal Ventures, to fight gender inequality.

Gates said her firm set three priorities for the investment:

“dismantling the barriers to women’s professional advancement”;

“fast-tracking women in sectors with outsized impact on our society—like technology, media, and public office”;

and “mobilizing shareholders, consumers, and employees to amplify external pressure on companies and organizations in need of reform.”

Calling the commitment “only a small fraction of what’s necessary,” Gates said she hoped that “others”—presumably, other billionaires—would also commit to making similar investments.