Purpose: This study examined whether monolingual German-speaking preschool children with developmental language disorder (DLD) were facilitated by the presence of case-marking cues in their interpretation of German subject and object "welcher" ("which")-questions, as reported for their typically developing peers. We also examined whether knowledge of case-marking and/or phonological working memory modulated children's ability to revise early assigned interpretations of ambiguous questions. Method: Sixty-three monolingual German-speaking children with and without DLD aged between 4;0 and 5;11 (years;months) participated in an offline picture selection task targeting the comprehension of "welcher"-questions in German. We manipulated question type (subject, object), case-marking transparency, and case-marking position within the question (sentence-initial/-final). Results: The typically developing children outperformed the children with DLD across conditions, and all children performed better on subject than on object "wh"-questions. Transparent and early cues elicited higher accuracy than late-arriving cues. For the DLD children, their working memory capacity explained their inability to revise early assigned interpretations to ambiguous questions, whereas their knowledge of case did not. Conclusions: The results suggest that disambiguating morphosyntactic cues can only partly facilitate comprehension of German "welcher"-questions in children with DLD, whose poor phonological working memory rather than their knowledge of case-marking mediates performance on these structures.