OK, I further simplified the test program to: - not use the event loop in the main process; use waitpid() - fail on first iteration You can see it here: https://gist.github.com/gists/2838734 The SIGCHLD is received, of course, but then libev fails to notify the child watcher in a timely manner. Instead, it delays the notification by 60 seconds (MAX_BLOCKTIME).