Tesla CEO Elon Musk bought a 9.2% stake in Twitter Inc., according to an SEC filing posted Monday.

Musk purchased roughly 73.5 million shares, making him the largest shareholder, The Associated Press reported Monday, citing the filing.

Musk has questioned whether Twitter “rigorously adheres to” the principle of “free speech.” Musk posted a poll on Twitter and 70.4% of respondents said Twitter does not.

“Given that Twitter serves as the de facto public town square, failing to adhere to free speech principles fundamentally undermines democracy. What should be done?” Musk then tweeted.

Musk also said he was “giving serious thought” to creating a new platform with “free speech.”

The investment is considered passive, according to the AP.