On 10 February 1662 he was forced to surrender Fort Zeelandia after a nine-month siege from a large Chinese force of 25,000 men and 1,000 ships under Koxinga. Coyett said that Chinese were "little better than poor specimens of very effeminate men", when he believed that there was no plan to invade Taiwan. The Dutch then changed their tune to "Formosa is lost" once the invasion was underway. With his army decisively crushed by the Chinese under Koxinga, Coyett left Taiwan after the Siege of Fort Zeelandia with enough supply to reach Batavia. After three years imprisonment he was tried for high treason, due to his failure to hold Taiwan or preserve vital commercial interests. Coyett was pardoned and exiled to Rosengain, the most eastern of the Banda Islands, before he was released in 1674. In 1684 he bought a house on Keizersgracht, on a spot where the Hemony brothers used to have their foundry.