This disclosure relates to performing bandwidth part activation in a cellular communication system. A wireless device may attach to a network via a cell that includes multiple bandwidth parts. The wireless device may receive an indication activating a non-default bandwidth part for the wireless device. A bandwidth part activation timer may be initiated based at least in part on activation of the non-default bandwidth part. At expiration of the bandwidth part activation timer, the wireless device may deactivate the non-default bandwidth part and activate a default bandwidth part if there is not a procedure to perform an uplink data transfer in progress. If there is a procedure to perform an uplink data transfer in progress at expiration of the bandwidth part activation timer, the procedure may be completed via the non-default BWP even after expiration of the bandwidth part activation timer.