This article reports an eye-tracking study on the native and non-native processing of case in Spanish. Twenty-four native and 27 first language (L1) German non-native speakers of Spanish were tested on their sensitivity to case marking violations involving structural case with objects of ditransitive verbs and to violations of inherent case for objects of transitive verbs (differential object marking; DOM). Both groups distinguished between grammatical and ungrammatical case marking for all sentence types in off-line acceptability judgments. In reading, however, the non-native speakers, unlike the native speakers, were sensitive only to violations of structural case marking with ditransitive verbs and the erroneous realization of DOM with inanimate objects. In contrast, they did not show processing slowdowns for the omission of DOM with animate objects. We interpret the asymmetry in non-native processing as reflecting sensitivity of the parser to grammatical feature hierarchies in that the parser licenses default case markings, yet flags feature clashes occasioned by the suppliance of erroneous inflectional forms with inherent case marking. We discuss the findings in the context of current approaches to second language (L2) acquisition and processing.