diff --git a/main.go b/main.go
index 7d3a6232..bd679e2c 100644
--- a/main.go
+++ b/main.go
@@ -260,33 +260,45 @@ func configureTLS(opts *server.Options) {
 }
 
 func configureClusterOpts(opts *server.Options) error {
-	if opts.ClusterListenStr == "" {
+	// If we don't have cluster defined in the configuration
+	// file and no cluster listen string override, but we do
+	// have a routes override, we need to report misconfiguration.
+	if opts.ClusterListenStr == "" && opts.ClusterHost == "" &&
+		opts.ClusterPort == 0 {
 		if opts.RoutesStr != "" {
 			server.PrintAndDie("Solicited routes require cluster capabilities, e.g. --cluster.")
 		}
 		return nil
 	}
 
-	clusterURL, err := url.Parse(opts.ClusterListenStr)
-	h, p, err := net.SplitHostPort(clusterURL.Host)
-	if err != nil {
-		return err
-	}
-	opts.ClusterHost = h
-	_, err = fmt.Sscan(p, &opts.ClusterPort)
-	if err != nil {
-		return err
-	}
-
-	if clusterURL.User != nil {
-		pass, hasPassword := clusterURL.User.Password()
-		if !hasPassword {
-			return fmt.Errorf("Expected cluster password to be set.")
+	// If cluster flag override, process it
+	if opts.ClusterListenStr != "" {
+		clusterURL, err := url.Parse(opts.ClusterListenStr)
+		h, p, err := net.SplitHostPort(clusterURL.Host)
+		if err != nil {
+			return err
+		}
+		opts.ClusterHost = h
+		_, err = fmt.Sscan(p, &opts.ClusterPort)
+		if err != nil {
+			return err
 		}
-		opts.ClusterPassword = pass
 
-		user := clusterURL.User.Username()
-		opts.ClusterUsername = user
+		if clusterURL.User != nil {
+			pass, hasPassword := clusterURL.User.Password()
+			if !hasPassword {
+				return fmt.Errorf("Expected cluster password to be set.")
+			}
+			opts.ClusterPassword = pass
+
+			user := clusterURL.User.Username()
+			opts.ClusterUsername = user
+		} else {
+			// Since we override from flag and there is no user/pwd, make
+			// sure we clear what we may have gotten from config file.
+			opts.ClusterUsername = ""
+			opts.ClusterPassword = ""
+		}
 	}
 
 	// If we have routes but no config file, fill in here.
diff --git a/server/opts.go b/server/opts.go
index 56ff4327..a0e61089 100644
--- a/server/opts.go
+++ b/server/opts.go
@@ -637,6 +637,9 @@ func MergeOptions(fileOpts, flagOpts *Options) *Options {
 	if flagOpts.ProfPort != 0 {
 		opts.ProfPort = flagOpts.ProfPort
 	}
+	if flagOpts.ClusterListenStr != "" {
+		opts.ClusterListenStr = flagOpts.ClusterListenStr
+	}
 	if flagOpts.RoutesStr != "" {
 		mergeRoutes(&opts, flagOpts)
 	}
diff --git a/server/opts_test.go b/server/opts_test.go
index 18adf2cf..70c1301b 100644
--- a/server/opts_test.go
+++ b/server/opts_test.go
@@ -276,6 +276,45 @@ func TestRouteFlagOverride(t *testing.T) {
 	}
 }
 
+func TestClusterFlagsOverride(t *testing.T) {
+	routeFlag := "nats-route://ruser:top_secret@127.0.0.1:7246"
+	rurl, _ := url.Parse(routeFlag)
+
+	// In this test, we override the cluster listen string. Note that in
+	// the golden options, the cluster other infos correspond to what
+	// is recovered from the configuration file, this explains the
+	// discrepency between ClusterListenStr and the rest.
+	// The server would then process the ClusterListenStr override and
+	// correctly override ClusterHost/ClustherPort/etc..
+	golden := &Options{
+		Host:               "127.0.0.1",
+		Port:               7222,
+		ClusterHost:        "127.0.0.1",
+		ClusterPort:        7244,
+		ClusterListenStr:   "nats://127.0.0.1:8224",
+		ClusterUsername:    "ruser",
+		ClusterPassword:    "top_secret",
+		ClusterAuthTimeout: 0.5,
+		Routes:             []*url.URL{rurl},
+	}
+
+	fopts, err := ProcessConfigFile("./configs/srv_a.conf")
+	if err != nil {
+		t.Fatalf("Received an error reading config file: %v\n", err)
+	}
+
+	// Overrides via flags
+	opts := &Options{
+		ClusterListenStr: "nats://127.0.0.1:8224",
+	}
+	merged := MergeOptions(fopts, opts)
+
+	if !reflect.DeepEqual(golden, merged) {
+		t.Fatalf("Options are incorrect.\nexpected: %+v\ngot: %+v",
+			golden, merged)
+	}
+}
+
 func TestRouteFlagOverrideWithMultiple(t *testing.T) {
 	routeFlag := "nats-route://ruser:top_secret@127.0.0.1:8246, nats-route://ruser:top_secret@127.0.0.1:8266"
 	rurls := RoutesFromStr(routeFlag)