Apparatuses, methods, and systems are disclosed for efficient cross-carrier scheduling of multiple slots. One apparatus includes a receiver that receives, from a base unit, a first control signal that indicates a maximum number of hybrid automatic repeat request (“HARQ”) processes. The receiver also receives a second control signal on a first carrier from the base unit that schedules a first number of slots on a second carrier. The apparatus includes a processor that aggregates every two or more of the scheduled first number of slots into a single HARQ process in response to the first number being larger than the maximum number of HARQ processes.