Methods, systems, and devices for wireless communication are described. A wireless device may receive a data transmission during a transmission time interval (TTI) that has one duration, and the device may transmit a responsive control message (e.g., acknowledgment information) in a subsequent TTI that has a different duration (e.g., a greater duration). In some cases, the control message may include bundled acknowledgment information for multiple downlink transmissions. The control message may, for instance, include acknowledgment information for data received during several TTIs having one duration bundled with acknowledgment information for data received during TTIs that have a different duration. The acknowledgment information may be compressed using, for example, a starting point and run length of consecutive negative acknowledgments.