diff --git a/main.go b/main.go
index 40ba744..51eb452 100644
--- a/main.go
+++ b/main.go
@@ -131,14 +131,22 @@ func secureRandBase64(length int) string {
 func main() {
 	var bind, certFile, keyFile, secret string
 	var showVersion bool
-	flag.BoolVar(&showVersion, "version", false, "show program's version number and exit")
-	flag.StringVar(&bind, "bind", defaultBind, "bind server to [HOSTNAME]:PORT")
-	flag.StringVar(&secret, "secret", "", "shared secret for client authentication")
-	flag.StringVar(&certFile, "cert", "", "file containing TLS certificate")
-	flag.StringVar(&keyFile, "key", "", "file containing TLS private key")
-	flag.Bool("invert", false, "obsolete, not used anymore")
-	flag.Int("interval", 0, "obsolete, not used anymore")
-	flag.Parse()
+	parseFlags := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
+	for _, fs := range [](*flag.FlagSet){parseFlags, flag.CommandLine} {
+		fs.BoolVar(&showVersion, "version", false, "show program's version number and exit")
+		fs.StringVar(&bind, "bind", defaultBind, "bind server to [HOSTNAME]:PORT")
+		fs.StringVar(&secret, "secret", "", "shared secret for client authentication")
+		fs.StringVar(&certFile, "cert", "", "file containing TLS certificate")
+		fs.StringVar(&keyFile, "key", "", "file containing TLS private key")
+	}
+	// ignore obsolete flags for backward compatibility, but don't show them in usage message
+	parseFlags.Usage = func() {}
+	parseFlags.Bool("invert", false, "")
+	parseFlags.Int("interval", 0, "")
+	if err := parseFlags.Parse(os.Args[1:]); err != nil {
+		flag.Usage()
+		os.Exit(2)
+	}
 	if showVersion {
 		fmt.Println(version)
 		return