In high stakes situations, people sometimes choke under pressure, performing below their abilities. Here, we suggest a novel mechanism to account for this paradoxical effect of motivation: the automatic adjustment of action vigour to potential reward. Although adaptive on average, this mechanism may impede fine motor control. Such detrimental effect was observed in three studies (n = 74 in total), using behavioural tasks where payoff depended on the precision of handgrip squeezing or golf putting. Participants produced more force for higher incentives, which aggravated their systematic overshooting of low-force targets. This reward bias was specific to action vigour, as reward did not alter action timing, direction or variability across trials. Although participants could report their reward bias, they somehow failed to limit their produced force. Such an automatic link between incentive and force level might correspond to a Pavlovian response that is counterproductive when action vigour is not instrumental for maximizing reward.