A buffer (72), (74), (76), (60), (78), (20), (82-90) has a number of entries for buffering items associated with data processing operations. Buffer control circuitry (100) has a redundant allocation mode in which, on allocating a given item to the buffer, the item is allocated to two or more redundant entries of the buffer. On reading or draining an item from the buffer, the redundant entries are compared and an error handling response is triggered if a mismatch is detected. By effectively reducing the buffer capacity, this simplifies testing for faults in buffer entries.