A packet switch includes a flow control circuit for preventing a downstream ingress port of the packet switch from providing a non-posted packet to an upstream egress port of the packet switch when a downstream egress port of the packet switch is congested. As a result, congestion is reduced in the downstream egress port. Additionally, congestion is reduced in an upstream ingress port of the packet switch that receives completion packets in response to non-posted packets output from the upstream egress port and provides the completion packets to the downstream egress port. Because congestion is reduced in the upstream ingress port, latency is reduced for a completion packet received at the upstream ingress port and provided to another downstream egress port of the packet switch in response to a non-posted packet provided from another downstream ingress port to the upstream egress port and output from the packet switch.