The finest graded US 1918 24c Inverted Jenny set a new auction record at Robert A Siegel in New York on May 31.
It realised $1.1m, edging out the previous record (set for the stamp taken from the next position on the sheet) by 20.1%.
Siegel explains: "This stamp has always been regarded as one of the finest from the original discovery sheet of 100.
"It is the only inverted jenny to have met the rigorous standards for the xf-superb 95 grade."
That status has translated into some impressive sums at auction. It last sold for $577,500 in 2005, resulting in growth of 7.3% per annum over the last 10 years.
The Inverted Jenny is America's most famous error stamp and one of very few known to people outside the hobby.
It's limited to a single sheet of 100 discovered in a post office in Washington, DC in 1918.
Most were broken up into singles and smaller multiples and sold.
The present specimen was formerly in the collection of philatelist and investor Robert Zoellner.
He bought it as a replacement for his previous Inverted Jenny, which was accidentally sucked up with a vacuum cleaner.
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