A pair of rare stamps bearing a picture of Chinese nationalist leader Sun Yat-sen sold for over $700,000 at a sale in Hong Kong on Saturday.

The 1941 blue and black stamps, rare because the picture of Sun is accidentally inverted, sold for HK$5.52 million ($707,700) to an anonymous phone bidder.

Auction house Zurich Asia said the price set a new “world auction record for any Republic of China stamp”, referring to the period of 1912 to 1949 in China, after the last imperial dynasty lost power and before the communists took over.

The pair came from the original sheet of 50 stamps that had the error.