This document describes extensions for the flow control of the Transmission Control Protocol (TCP) that avoid interactions with fast startup congestion control mechanisms, in particular the Quick-Start TCP extension. Quick-Start is an optional TCP extension that allows to start data transfers with a large congestion window, using feedback of the routers along the path. This can avoid the time consuming Slow-Start, provided that the TCP flow control is not a limiting factor. There are two potential interactions between the TCP flow control and congestion control schemes without the standard Slow-Start: First, receivers might not allocate a sufficiently large buffer space after connection setup, or they may advertise a receive window implicitly assuming the Slow-Start behavior on the sender side. This document therefore provides guidelines for buffer allocation in hosts supporting the Quick-Start extension. Second, the TCP receive window scaling mechanism can prevent fast startups immediately after the initial three-way handshake connection setup. This document describes a simple solution to overcome this problem.