A method, performed by a user equipment, UE, for communicating with a first eNode-B, eNB, and a second eNB simultaneously in a wireless communication system, comprising: configuring (S1301) that uplink, UL, data is only to be transmitted to the first eNB, if an amount of data available for transmission in a packet data convergence protocol, PDCP, entity, DATP, is less than a threshold; receiving (S1303) PDCP data from an upper layer; upon the amount of DATP becoming larger than or equal to the threshold, transmitting (S1305) a buffer status report, BSR, to request an UL grant to the second eNB; after transmitting (S1305) the BSR to the second eNB, receiving (S1307) the UL grant from the second eNB; and if between the step of transmitting (S1305) the BSR and the step of receiving (S1307) the UL grant, the UE has transmitted a part of the DATP to the first eNB using another UL grant received from the first eNB, and therefore the amount of DATP has become less than the threshold: transmitting (S1309) to the second eNB using the UL grant, that PDCP data whose size has been indicated to the second eNB by the BSR, even if the amount of DATP at the time of transmission of said PDCP data is less than the threshold; and not transmitting (S1311) to the second eNB using the UL grant, that PDCP data whose size has not been indicated to the second eNB by the BSR, if the amount of DATP at the time of transmission of said PDCP data is less than the threshold. configuring (S1301) that uplink, UL, data is only to be transmitted to the first eNB, if an amount of data available for transmission in a packet data convergence protocol, PDCP, entity, DATP, is less than a threshold; receiving (S1303) PDCP data from an upper layer; upon the amount of DATP becoming larger than or equal to the threshold, transmitting (S1305) a buffer status report, BSR, to request an UL grant to the second eNB; after transmitting (S1305) the BSR to the second eNB, receiving (S1307) the UL grant from the second eNB; and if between the step of transmitting (S1305) the BSR and the step of receiving (S1307) the UL grant, the UE has transmitted a part of the DATP to the first eNB using another UL grant received from the first eNB, and therefore the amount of DATP has become less than the threshold: transmitting (S1309) to the second eNB using the UL grant, that PDCP data whose size has been indicated to the second eNB by the BSR, even if the amount of DATP at the time of transmission of said PDCP data is less than the threshold; and not transmitting (S1311) to the second eNB using the UL grant, that PDCP data whose size has not been indicated to the second eNB by the BSR, if the amount of DATP at the time of transmission of said PDCP data is less than the threshold. transmitting (S1309) to the second eNB using the UL grant, that PDCP data whose size has been indicated to the second eNB by the BSR, even if the amount of DATP at the time of transmission of said PDCP data is less than the threshold; and not transmitting (S1311) to the second eNB using the UL grant, that PDCP data whose size has not been indicated to the second eNB by the BSR, if the amount of DATP at the time of transmission of said PDCP data is less than the threshold. <EOS>