We report two case studies of aphasic patients with a working-memory impairment due to reduced storage in the phonological buffer. The two patients display excellent performance in phonological discrimination tasks as long as the tasks do not involve a memory load. We then show that their performance drops when they have to maintain fine-grained phonological information for sentence comprehension: They are impaired at mispronunciation detection and at comprehending sentences involving minimal word pairs. We argue that the phonological buffer plays a role in sentence perception during the phonological analysis of the speech stream: It sustains the temporary storage of phonological input in order to check and resolve phonological ambiguities, and it also allows reexamination of the phonological input if necessary.