Calling pause_reading()/resume_reading() on a _ProactorReadPipeTransport will result in an InvalidStateError('Result is not ready.') from a future if no read has been issued yet. The reason is that resume_reading() will schedule _loop_reading() a second time on the event loop. For example, currently aiomysql always fails to connect using a ProactorEventLoop on Windows because it calls pause_reading()/resume_reading() to set TCP_NODELAY on the socket just after connecting and before any read is performed.