One of the most intriguing questions in the investigation of second-language acquisition concerns the role of learners' first language (L1). Comparing learners of different backgrounds (L1 German vs. L1 Romance languages), we aim to explore the acquisition of tense and aspect features in Spanish as a second language (L2). Findings show that the L1 indeed has an undeniable effect also visible in language interpretation. These results are discussed in the light of the Feature Reassembly Hypothesis and a version of the microparametric approach to cross-linguistic differences. Different from the participants with a Romance language who can rely on the great similarities between Spanish and their L1, the German learners show a learning strategy clearly based on their L1. In German, aspect is not expressed by verbal morphology but by lexical means such as adverbs. This fact leads to an adverb-based learning strategy that (different from what has been found among learners of L2 Spanish in previous studies) not only blurs an underlying competence but prevents the complete acquisition of the underlying features. Other external variables, such as immersion, do not change the outcome considerably.