Google ( GOOG) filed to sell 5.3 million shares to mostly accommodate index funds needing a piece of the company as it prepares to join the S&P 500 index.

Based on Wednesday's closing price of $394.98, Google's offering would raise about $2.1 billion.

Google said in a filing with the Securities and Exchange Commission that it will use proceeds from the sale for "general corporate purposes," including potential acquisitions. But the company added that there were "no current agreements or commitments with respect to any material acquisitions."

Following the announcement, the company's shares slipped $12.07, or 3.1%, to $382.91 in after-hours trading on Instinet.

Google's SEC filing indicated the company will sell the latest round of stock some time next month.