This paper addresses the issue of whether negative sentences containing auxiliary "do" in L1 and L2 English share the same underlying syntactic representation. To this end, I compare the negative sentences produced by 77 bilingual (Spanish/Basque) L2 learners of English with the corresponding data available for L1 acquirers reported on in Schutze (Carson, The status of he/she don't and theories of root infinitives, 2001), under the assumption that L1 and L2 grammars may be underspecified for Tense and/or Agreement features. I conclude that, despite similarities in the type of errors children and L2 learners produce, the L2 data do not show evidence of underspecification. Rather, it appears that L2 learners use a lexical strategy whereby they adopt "don't" as an independent preverbal negative marker.