Language aptitude remains one of the most understudied predictor variables in L1 attrition research. The current study seeks to address this gap by investigating the effects of language aptitude on L1 retention in late attriters. Forty L1 Spanish-L2 Swedish bilinguals living in Sweden participated in the study, along with 20 functionally monolingual L1 speakers of Spanish. L1 proficiency was measured by means of a grammaticality judgement test (GJT) and language aptitude data were obtained through the "LLAMA Language Aptitude Test" (Meara 2005). Additional data on the participants' linguistic background were also collected. Results revealed a robust difference in GJT scores between the bilinguals and the control group. However, degree of language aptitude was not found to exert a significant influence on the bilinguals' GJT performance. Instead, the only significant predictor for GJT performance was linguistic identification, showing that those participants with strong L1 identification were more accurate in judging L1 grammaticality. The lack of aptitude effects on L1 attrition is discussed against the background of age-related attrition susceptibility.