Previous research has shown L1 attrition to be restricted to structures at the interfaces between syntax and pragmatics, but not to occur with syntactic properties that do not involve such interfaces ("Interface Hypothesis", Sorace and Filiaci in "Anaphora resolution in near-native speakers of Italian." "Second Lang Res" 22: 339-368, 2006). The present study tested possible L1 attrition effects on a syntax-semantics interface structure [Differential Object Marking (DOM) using the Spanish personal preposition] as well as the effects of recent L1 re-exposure on the potential attrition of these structures, using offline and eye-tracking measures. Participants included a group of native Spanish speakers experiencing attrition ("attriters"), a second group of attriters exposed exclusively to Spanish before they were tested, and a control group of Spanish monolinguals. The eye-tracking results showed very early sensitivity to DOM violations, which was of an equal magnitude across all groups. The off-line results also showed an equal sensitivity across groups. These results reveal that structures involving "internal" interfaces like the DOM do not undergo attrition either at the processing or representational level.