Two days after announcing plans to donate $45 billion over time to his family foundation, Facebook CEO Mark Zuckerberg responded to criticism about his philanthropic ambitions.

In a Facebook post on Thursday, he pushed back against accusations that he had structured his foundation, not so much as a charity, but as a vehicle for evading taxes and making financially motivated investments under the guise of doing good.

Zuckerberg created the foundation as a limited liability corporation instead of a traditional foundation. He said that he and his wife, Priscilla Chan, would fund it with 99% of his wealth, made from a huge stake in the social network he co-founded.