Methods, systems, and devices for wireless communication are described. A user equipment (UE) may transmit a control message during a special subframe of a radio frame. The UE may determine a payload size of the control message according to a radio resource configuration, or the UE may determine a payload size based on a number of bits associated with information to be sent in the control message. The UE may identify uplink resources of the special subframe to use for the control message based on explicit signaling or implicitly based on information to be sent in the control message. Designated resources for control message transmissions in a special subframe may remain the same or may change in subsequent transmission opportunities. The UE may determine to use the same or different resources of a special subframe in a subsequent transmission opportunity depending on when the UE receives downlink messages.