A rare 1917 Italian Peking 40c on 50c error of surcharge postage stamp features in an online auction, which is closing tomorrow (October 23).
The mint condition violet example, which boasts full perforations and fresh colours, is only marred by some light hinging.
Described by the auction house as a "major rarity of China philately", it is expected to achieve between £7,000-8,000 ($11,225-12,750).
The stamp comes from the Italian post office in Peking (Pechino in Italian), now known as Beijing.
The Peking office was one of two Italian post offices in the country, the other was based in Tientsin. Used for sending military and diplomatic mail, both offices produced their own stamps between 1917 and 1922.
The Sassone catalogue offers a €25,000 (£20,000) valuation for a top condition specimen.
We are delighted to offer you our own rarity of the far east: the unique 96c olive-bistre block of four - the most important item in Hong Kong philately.
You can view all our philatelic items for sale here.
Tomorrow's sale will also feature a superb complete set of the 1941 Italian occupation in Ithaca issue, which includes the rare 80 lira violet and brown. It has a £20,000-25,000 ($31,500-39,250) estimate.
"Only a handful of this issue are in existence and this complete set plus the rarely seen 80l comes complete with a 1986 Bolaffi colour photo certificate," says the auction house.
We will bring you full results of the sale later in the week.
To keep abreast of all the latest from the world's stamp auctions sign up to our free weekly newsletter.