A recent proposal attributes morphosyntactic issues in L2 to lexical factors (Grüter et al. 2012; Hopp 2013). According to this lexical account, issues with gender agreement are caused by gender assignment issues – a failure to assign a word to a target-like class. We elaborate on this idea by exploring three potential cues to gender assignment: 1) semantic gender relating to sex (e.g. ‘girl’ vs. ‘boy’) 2) morphophonological cues, and 3) morphosyntactic agreement cues. Semantic and morphophonological cues may facilitate gender agreement only for a subset of nouns, whereas agreement cues can do so for all nouns, including opaque gender nouns that do not have semantic gender.Seventeen low proficiency and sixteen high proficiency L1 English L2 Spanish speakers and eighteen native Spanish controls judged the grammaticality of 60 experimental sentences. We compared participants’ gender agreement accuracy and reaction times (RTs) on experimental items with and without semantic gender, and with and without transparent gender morphemes. Semantic gender did not serve as a cue for gender assignment/agreement; instead, it slowed down RTs in high proficiency and control participants. Morphophonological cues significantly increased accuracy and decreased RTs in all groups. Finally, agreement cues did not seem to help low proficiency learners, since their accuracy on opaque nouns was barely above chance. By contrast, high proficiency learners exhibited native-like accuracy on opaque nouns. These findings support the lexical accounts of L2 gender agreement difficulties, adding more data to the growing body of research in this field.