Success or failure in L2 acquisition has been attributed to different factors, such as the linguistic domain involved, (the absence of) instruction or positive or negative transfer. Whereas in most of the literature these factors are studied separately, in this paper we investigate the relative impact of each of them, analyzing the L2 acquisition of the French quantitative pronoun en by native speakers of Dutch. On the basis of acquisition data elicited in a Grammaticality Judgment Task, we show that the L2 acquisition of en proceeds very slowly. We argue that this is mainly caused by the presence of a similar, but not completely equivalent pronoun in Dutch.