Methods, systems, and devices for wireless communications are described. A user equipment (UE) may indicate support of an extended cyclic prefix (ECP), where a duration of the ECP or transmitting the ECP is based on the indication. In some cases, the UE may receive an uplink grant to transmit an uplink message with an indication of the ECP, and the UE may transmit the ECP and uplink message according to a timeline based in part on the ECP. Additionally or alternatively, an uplink channel allocation indicated in the uplink grant may include a starting point for the ECP, where the UE transmits the ECP at the starting point. In some cases, the UE may multiplex uplink control information (UCI) in the uplink channel based on a timeline that is based in part on the ECP.