Computing apparatus includes a host computer, including at least first and second host bus interfaces. A network interface controller (NIC) includes a network port, for connection to a packet communication network, and first and second NIC bus interfaces, which communicate via first and second peripheral component buses with the first and second host bus interfaces, respectively. Packet processing logic, in response to packets received through the network port, writes data to the host memory concurrently via both the first and second NIC bus interfaces in a sequence of direct memory access (DMA) transactions, and after writing the data in any given DMA transaction, writes a completion report to the host memory with respect to the given DMA transaction while verifying that the completion report will be available to the CPU only after all the data in the given DMA transaction have been written to the host memory.