The Dutch intentions were anticipated by the Spanish. According to Joseph de La Pise, a French jurist hired by Maurice's half brother and successor Frederick Henry to write a history of the Princes of Orange,Frijhoff, p. 95 Mondragón had learned of the ambush from English soldiers who had deserted from the Dutch colours,De La Pise, p. 641 but the Italian Jesuit Angello Gallucci claims that it was Spanish spies who informed Mondragón,Gallucci, p. 291 who had used spies to gather information on the enemy since the siege of Zierikzee, in 1576.Salcedo y Ruiz, p. 183. In any case, the Spanish general took measures to turn Nassau's surprise into a trap. The convoy, normally guarded by 300 infantry and 150 cavalry, was reinforced by 300 musketeers and a large force of cavalry under Mondragón's lieutenant, Juan de Córdoba.
