diff --git a/pkg/webserver/webserver.go b/pkg/webserver/webserver.go
index 3fd60bc8e..1d183648e 100644
--- a/pkg/webserver/webserver.go
+++ b/pkg/webserver/webserver.go
@@ -29,6 +29,8 @@ import (
 	"os"
 	"strings"
 	"time"
+
+	"camlistore.org/third_party/github.com/bradfitz/runsit/listen"
 )
 
 var Listen = flag.String("listen", "", "host:port to listen on, or :0 to auto-select")
@@ -99,23 +101,27 @@ func (s *Server) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
 // Listen starts listening on the given host:port string.
 // If listen is empty the *Listen flag will be used instead.
-func (s *Server) Listen(listen string) error {
+func (s *Server) Listen(addr string) error {
 	if s.listener != nil {
 		return nil
 	}
 
 	doLog := os.Getenv("TESTING_PORT_WRITE_FD") == "" // Don't make noise during unit tests
-	if listen == "" {
+	if addr == "" {
 		if *Listen == "" {
 			return fmt.Errorf("Cannot start listening: host:port needs to be provided with the -listen flag")
 		}
-		listen = *Listen
+		addr = *Listen
 	}
 
-	var err error
-	s.listener, err = net.Listen("tcp", listen)
+	var laddr listen.Addr
+	err := laddr.Set(addr)
 	if err != nil {
-		log.Fatalf("Failed to listen on %s: %v", listen, err)
+		return err
+	}
+	s.listener, err = laddr.Listen()
+	if err != nil {
+		log.Fatalf("Failed to listen on %s: %v", addr, err)
 	}
 	base := s.BaseURL()
 	if doLog {
diff --git a/third_party/github.com/bradfitz/runsit/listen/listen.go b/third_party/github.com/bradfitz/runsit/listen/listen.go
new file mode 100644
index 000000000..c7547b08f
--- /dev/null
+++ b/third_party/github.com/bradfitz/runsit/listen/listen.go
@@ -0,0 +1,125 @@
+package listen
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"net"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func NewFlag(flagName, defaultValue string, serverType string) *Addr {
+	addr := &Addr{
+		s: defaultValue,
+	}
+	flag.Var(addr, flagName, Usage(serverType))
+	return addr
+}
+
+// Usage returns a descriptive usage message for a flag given the name
+// of thing being addressed.
+func Usage(name string) string {
+	if name == "" {
+		name = "Listen address"
+	}
+	if !strings.HasSuffix(name, " address") {
+		name += " address"
+	}
+	return name + "; may be port, :port, ip:port, FD:<fd_num>, or ADDR:<name> to use named runsit ports"
+}
+
+// Addr is a flag variable.  Use like:
+//
+// var webPort listen.Addr
+// flag.Var(&webPort, "web_addr", listen.Usage("Web server address"))
+// flag.Parse()
+// webListener, err := webPort.Listen()
+type Addr struct {
+	s   string
+	ln  net.Listener
+	err error
+}
+
+func (a *Addr) String() string {
+	return a.s
+}
+
+// Set implements the flag.Value interface.
+func (a *Addr) Set(v string) error {
+	a.s = v
+
+	// Try the requested port by runsit port name first.
+	fd, ok, err := namedPort(v)
+	if err != nil {
+		return err
+	}
+	if ok {
+		return a.listenOnFD(fd)
+	}
+
+	if strings.HasPrefix(v, "FD:") {
+		fdStr := v[len("FD:"):]
+		fd, err := strconv.ParseUint(fdStr, 10, 32)
+		if err != nil {
+			return fmt.Errorf("invalid file descriptor %q: %v", fdStr, err)
+		}
+		return a.listenOnFD(uintptr(fd))
+	}
+
+	ipPort := v
+	if isPort(v) {
+		ipPort = ":" + v
+	}
+
+	_, _, err = net.SplitHostPort(ipPort)
+	if err != nil {
+		return fmt.Errorf("invalid PORT or IP:PORT %q: %v", v, err)
+	}
+	a.ln, err = net.Listen("tcp", ipPort)
+	return err
+}
+
+func isPort(s string) bool {
+	_, err := strconv.ParseUint(s, 10, 16)
+	return err == nil
+}
+
+func (a *Addr) listenOnFD(fd uintptr) (err error) {
+	f := os.NewFile(fd, fmt.Sprintf("fd #%d from runsit parent", fd))
+	a.ln, err = net.FileListener(f)
+	return
+}
+
+func namedPort(name string) (fd uintptr, ok bool, err error) {
+	s := os.Getenv("RUNSIT_PORTFD_" + name)
+	if s == "" {
+		return
+	}
+	u64, err := strconv.ParseUint(s, 10, 32)
+	if err != nil {
+		return
+	}
+	return uintptr(u64), true, nil
+}
+
+var _ flag.Value = (*Addr)(nil)
+
+// Listen returns the address's TCP listener.
+func (a *Addr) Listen() (net.Listener, error) {
+	// Start the listener now, if there's a default
+	// and nothing's called Set yet.
+	if a.err == nil && a.ln == nil && a.s != "" {
+		if err := a.Set(a.s); err != nil {
+			return nil, err
+		}
+	}
+	if a.err != nil {
+		return nil, a.err
+	}
+	if a.ln != nil {
+		return a.ln, nil
+	}
+	return nil, errors.New("listen: no error or listener")
+}