A rare US stamp which was mistakenly printed with an illustration of an upside down plane has been sold for £184,000 at auction in Warwick.
The 1918 Inverted Jenny is one of the icons of world stamp collecting, auctioneers Warwick & Warwick said.
Its eventual sale price, to an unnamed bidder, beat the £150,000 it was expected to fetch.
The stamp shows a Curtiss JN-4 - known as a Jenny - used for training pilots during World War I.
One hundred of the erroneous stamps went on sale in 1918.
They were snapped up by a stockbroker's clerk, William T Robey, at a post office in Washington DC, the auctioneers said.
The error happened because the stamp's two colours, red for the frame and a blue central image, were printed in two separate operations.
Warwick & Warwick said Mr Robey was keen on sending first day covers to his friends and went to buy several examples of the 24 cent airmail stamp.
When he saw a sheet of 100 stamps showing the aeroplane upside down, he handed over $24 and bought the whole lot.
By 1940 single stamps were changing hands at $4,100 (£2,912) and in 2007 two were sold which achieved $825,000 (£585,910) and $850,000 (£603,665) before the addition of the buyer's premium, Warwick & Warwick said.
Director Colin Such said that he felt it was "an honour and a privilege" for the company to be selected to auction such a rare and valuable stamp.