It’s the financial windfall nerd dreams are made of. A Norwegian man who bought $25 of  Bitcoinin 2009 found four years later that his off-the-cuff investment had ballooned to a fortune worth $850,000.

The story starts when Kristoffer Koch was a student researching a paper about encryption. He came across the online currency Bitcoin, thought it seemed like a novel idea and bought about 150 kroners’ worth — around $25 by today’s conversion rates. Then Koch forgot all about the purchase, Norway’s public broadcasting company NRK reported, according to a Google translation.

Fast forward to this spring, when Bitcoin has been all over the news — both as a topic on its own, as well as a side player in major stories such as the rise and fall of the Silk Road online narcotics marketplace. The topic rang a bell for Koch, who recalled his impulsive purchase from back in 2009. He was able to remember his password, and check in on his little Bitcoin collection.

When Koch opened his digital wallet, he said he found 5,000 Bitcoins worth 5 million kroner, or about $850,000. He exchanged a fifth of the treasure trove for cash, then used that to buy an apartment in a posh Oslo neighborhood.

Koch said his girlfriend has long criticized his habit of buying technology-related odds and ends that he never ends up using. But now?

She’ll let him buy what he wants, Koch told NRK.