The present disclosure may enable a buffer to accommodate HARQ processes for transmissions with different TTIs when the UE is configured for legacy communications and ULL communications. The apparatus may allocate a first number of HARQ IDs to a first portion of a buffer, the first number of HARQ IDs being associated with a first transmission TTI HARQ process. In addition, the apparatus may allocate a second number of HARQ IDs to a second portion of the buffer. In an aspect, the second number of HARQ IDs may be associated with a second TTI HARQ process. In addition, the first portion and second portion may not change a total buffer size. The apparatus may also receive a HARQ response associated with a HARQ ID allocated to the first portion or the second portion.