Higgins's (2000) regulatory fit theory proposes that a fit between one's regulatory state and strategic means for reaching a goal increases motivational strength and engagement. This study investigates how regulatory fit affects the L2 acquisition of lexical stress in an authentic learning context. Ninety EFL students were assigned to either gain frame or loss frame conditions. They engaged in speech practice in which they mimicked a model speech in English to win a chance to enter a prize raffle. The reward system was framed differently in the two framing conditions, with the intention of eliciting the participants' use of eager or vigilant strategies, thus creating fit and nonfit conditions. Acquisition of lexical stress was assessed using pre- and posttest scores. Multiple regression analysis showed no regulatory fit effects and no loss frame effects but did show a significant beneficial effect of the gain frame on the acquisition of lexical stress.