A method is described of reporting control information in a wireless communication system. A user equipment (UE) supporting at least one cell including a primary cell selects a physical uplink control channel (PUCCH) format among a plurality of PUCCH formats including a first PUCCH format and a second PUCCH format. The first PUCCH format is selected if the UE receives a first physical downlink shared channel (PDSCH) in one of M downlink time division duplex (TDD) subframes on the primary cell. The UE receives a second PDSCH with a downlink assignment index (DAI) in one of the M downlink TDD subframes on the primary cell. The UE does not receive a first physical downlink control channel (PDCCH) corresponding to the first PDSCH on the primary cell. The UE receives a second PDCCH corresponding to the second PDSCH, and transmits a positive-acknowledgement/negative-acknowledgement (ACK/NACK) signal by using the selected PUCCH format.