Non-word repetition tasks are widely used to assess phonological short-term memory (PSTM). Results of previous research on the performance of monolingual and bilingual children in PSTM tasks are inconclusive. Although in some studies bilinguals did outperform monolinguals in the repetition of non-words, most studies reported comparatively weak results of bilingual children, especially when they were tested in their L2. In this study, four-year-old monolingual and bilingual children acquiring German (N = 1,441) were tested with both German-based (GBNW) and quasi-universal non-words (QUNW). It was hypothesized that bilinguals would outperform monolinguals both in (a) GBNW under the condition of comparable German language skills and (b) QUNW without any preconditions because QUNW do not presuppose a good command of German. Bilinguals yielded significantly lower results in GBNW, but not in QUNW. After the exclusion of children with limited German language skills from both groups, bilinguals outperformed monolinguals in both tasks, especially in QUNW. It can be assumed that bilingualism puts higher demands on PSTM than monolingualism and thus contributes to its faster development. Unnecessary medical examinations and therapies that are sometimes prescribed to bilinguals due to a poor performance in German-based PSTM tasks can be avoided if QUNW are used instead of language-specific items.