Working memory (WM) as a key component of language aptitude has become a topical issue, with some going so far as to argue that WM can replace language aptitude. Research that specifically investigates the relationship between WM and language aptitude is rather limited. This study explores the determinants of language aptitude, with a focus on WM capacity. A total of 72 Turkish university students with advanced English proficiency participated in the study. The instruments used to measure WM capacity included a reading span task in L1 (Turkish) and L2 (English) and an operation span task in L1. Language aptitude was measured with a computerised aptitude test: the LLAMA. A correlation analysis revealed that WM capacity correlated with the language aptitude total score rather than language aptitude subcomponents, with the exception of grammatical inferencing. A principal component analysis further showed WM and language aptitude as separate constructs. In addition, two distinct factors emerged under the aptitude construct, which can be attributed to the modality of the aptitude subtests. The results suggest that WM capacity still has a key role in the renewed aptitude construct, yet these two cognitive abilities are not interchangeable.