Updated from 9:49 a.m.

Microsoft

(MSFT) - Get Report

just can't buy back enough stock.

The Redmond, Wash., software giant added $16.2 billion to its existing buyback plan Friday after a $20 billion Dutch auction self-tender fell way short of targets.

The news comes as Microsoft said it expects to repurchase 155 million shares at $24.75 each in a previously disclosed Dutch auction self-tender. That plan will cost $3.8 billion. Microsoft said last month it would buy back as many as 808 million shares in a $20 billion buyback plan.

Microsoft

said last month it would also start on buyback of up to $20 billion to be completed by 2011.

But with the Dutch auction having come up $16.2 billion short, Microsoft is simply adding those shares to its five-year plan. The company now is due to repurchase some $36 billion worth of stock by June 30, 2011.

Microsoft said last month that its earlier buyback plan covering $30 billion in stock has been completed.

Shares rose 46 cents early Friday to $25.16.