A method for data transfer includes transmitting a sequence of data packets, including at least a first packet and a second packet transmitted subsequently to the first packet, from a first computer over a network to a second computer in a single remote direct memory access (RDMA) data transfer transaction. Upon receipt of the second packet at the second computer without previously having received the first packet, a negative acknowledgment (NAK) packet is sent from the second computer over the network to the first computer, indicating that the first packet was not received. In response to the NAK packet, the first packet is retransmitted from the first computer to the second computer without retransmitting the second packet.