In 1488 he was on a commission to inspect the ordnance at Calais, and in 1491 was made a Knight of the Garter. In the following year he was placed in command of fifteen hundred men sent to aid the Emperor Maximilian against his rebellious subjects in the Netherlands. The rebels, under the leadership of Ravenstein, held Bruges, Damme, and Sluys, where they fitted out ships to prey on English commerce. Poynings first cleared the sea of the privateers, and then laid siege to Sluys in August, while the Duke of Saxony blockaded it on land. After some hard fighting the two castles defending the town were taken, and the rebels entered into negotiations with Poynings to return to their allegiance. Poynings then joined Henry VII before Boulogne, but the French war was closed almost without bloodshed by the treaty of Etaples on 3 November.