diff --git a/web/web.go b/web/web.go
index 0befd55e91..b26f7e71bf 100644
--- a/web/web.go
+++ b/web/web.go
@@ -15,6 +15,7 @@ package web
 
 import (
 	"code.google.com/p/gorest"
+	"flag"
 	"github.com/prometheus/client_golang"
 	"github.com/prometheus/prometheus/storage/metric"
 	"github.com/prometheus/prometheus/web/api"
@@ -22,6 +23,11 @@ import (
 	_ "net/http/pprof"
 )
 
+// Commandline flags.
+var (
+	listenAddress = flag.String("listenAddress", ":9090", "Address to listen on for web interface.")
+)
+
 func StartServing(persistence metric.MetricPersistence) {
 	gorest.RegisterService(api.NewMetricsService(persistence))
 	exporter := registry.DefaultRegistry.YieldExporter()
@@ -30,5 +36,5 @@ func StartServing(persistence metric.MetricPersistence) {
 	http.Handle("/metrics.json", exporter)
 	http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("web/static"))))
 
-	go http.ListenAndServe(":9090", nil)
+	go http.ListenAndServe(*listenAddress, nil)
 }