diff --git a/examples/cert.go b/examples/cert.go
index 9ab80af..9d04cd8 100644
--- a/examples/cert.go
+++ b/examples/cert.go
@@ -7,6 +7,7 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/pem"
+	"fmt"
 	"log"
 	"os"
 	"time"
@@ -15,9 +16,20 @@ import (
 )
 
 func main() {
-	host := "localhost"
-	duration := 365 * 24 * time.Hour
-	cert, err := gemini.NewCertificate(host, duration)
+	if len(os.Args) < 3 {
+		fmt.Printf("usage: %s [hostname] [duration]\n", os.Args[0])
+		os.Exit(1)
+	}
+	host := os.Args[1]
+	duration, err := time.ParseDuration(os.Args[2])
+	if err != nil {
+		log.Fatal(err)
+	}
+	options := gemini.CertificateOptions{
+		DNSNames: []string{host},
+		Duration: duration,
+	}
+	cert, err := gemini.CreateCertificate(options)
 	if err != nil {
 		log.Fatal(err)
 	}