Example implementations relate to packet transmission credit allocation. In some examples, a system may include a processing resource and a memory resource storing instructions executable by the processing resource to allocate a first amount of packet transmission credits from a destination node to a source node; determine a modification to the first amount of packet transmission credits allocated from the destination node to the source node based on a comparison of a quantity of redeemed packet transmission credits by the source node to a packet transmission credit threshold of the source node; adjust the modification based on a condition at a buffer associated with the destination node; and apply the adjusted modification to the first amount of packet transmission credits to produce a second amount of packet transmission credits to allocate from the destination node to the source node.