A method for communication includes storing packets received from a sending node over a communication link in a receive buffer of a receiving node. The receive buffer includes one or more blocks having a first block size. A first credit count, corresponding to a number of available blocks in the receive buffer, is derived. The first credit count is converted to a second credit count so as to represent an available space in the receive buffer in accordance with a second block size, which is different from the first block size. A transmission rate of the sending node is controlled by publishing the second credit count to the sending node over the communication link.