FORTUNE — Facebook has significantly increased the size of its initial public offering, just two days before it is expected to begin trading on the NASDAQ.

According to an amended registration document, Facebook FB will now offer over 421 million shares to investors. That is around 83.8 million shares more than originally offered, which would work out to another $3.19 billion in proceeds if Facebook prices at the top of its $35-$38 per share offering range.

The entire offering now would raise over $16 billion at the $38 per share price, which would make it the largest-ever technology IPO. The current leader is AT&T Wireless, which raised over $10 billion in 2010. It also would become the third-largest IPO ever on a U.S. exchange, following Visa’s V $19.65 billion offering in March 2008 and General Motors GM raising $18.145 billion in November 2010.

Facebook also increased its “green-shoe” — or the number of extra shares underwriters can sell if the deal is oversubscribed — from 50.61 million to 63.19 million. Expectations are that there is enough demand that underwriters will use most, if not all, of their over-allotment.

It is worth noting that the share increase would not affect Facebook’s valuation, as the extra shares are simply being reallocated out of the company’s existing share count. More specifically, certain insiders are selling more. Venture capital firm Accel Partners, for example, has increased its number of shares being sold in the IPO from 38.19 million to 49 million. DST group from 26.25 million to 45.66 million, while its Mail.ru affiliate has bumped its number from 11.27 million to 19.6 million.

T. Rowe Price remains Facebook’s largest institutional holder to not sell any shares via the IPO.

Facebook’s amended filing does not mention yesterday’s news that General Motors plans to stop advertising on Facebook, after determining that paid ads on the site were not influencing customer behavior. GM spent around $10 million last year on Facebook ads.

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