Berkshire Hathaway purchased a small stake in Sirius XM, causing the stock to jump 9.1%.
The purchase was likely made by investment manager Ted Weschler, not Warren Buffett.
The new position is very small for Buffett, who typically makes purchases of at least $3 billion.
Sirius XM has a high short-interest ratio, which can lead to volatile stock movements.
The jump in Sirius stock is causing financial pain for arbitragers and other investors.