diff --git a/cmd/pkgsite/main.go b/cmd/pkgsite/main.go
index 0110008..95895fa 100644
--- a/cmd/pkgsite/main.go
+++ b/cmd/pkgsite/main.go
@@ -23,7 +23,9 @@
 import (
 	"context"
 	"flag"
+	"fmt"
 	"net/http"
+	"os"
 	"strings"
 	"time"
 
@@ -47,15 +49,20 @@
 )
 
 func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "usage: %s [flags] [PATHS ...]\n", os.Args[0])
+		fmt.Fprintf(flag.CommandLine.Output(), "    where PATHS is a single path or a comma-separated list\n")
+		flag.PrintDefaults()
+	}
 	flag.Parse()
 	ctx := context.Background()
 
-	paths := flag.Arg(0)
-	if paths == "" {
-		paths = "."
+	paths := collectPaths(flag.Args())
+	if len(paths) == 0 {
+		paths = []string{"."}
 	}
 
-	server, err := newServer(ctx, strings.Split(paths, ","), *gopathMode)
+	server, err := newServer(ctx, paths, *gopathMode)
 	if err != nil {
 		log.Fatalf(ctx, "newServer: %v", err)
 	}
@@ -66,6 +73,14 @@
 	log.Fatal(ctx, http.ListenAndServe(*httpAddr, mw(router)))
 }
 
+func collectPaths(args []string) []string {
+	var paths []string
+	for _, arg := range args {
+		paths = append(paths, strings.Split(arg, ",")...)
+	}
+	return paths
+}
+
 func newServer(ctx context.Context, paths []string, gopathMode bool) (*frontend.Server, error) {
 	getters := buildGetters(ctx, paths, gopathMode)
 	lds := fetchdatasource.Options{
diff --git a/cmd/pkgsite/main_test.go b/cmd/pkgsite/main_test.go
index f0db81d..b749076 100644
--- a/cmd/pkgsite/main_test.go
+++ b/cmd/pkgsite/main_test.go
@@ -10,6 +10,8 @@
 	"net/http"
 	"net/http/httptest"
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 func Test(t *testing.T) {
@@ -27,3 +29,11 @@
 		t.Errorf("%q: got status code = %d, want %d", "/testmod", w.Code, http.StatusOK)
 	}
 }
+
+func TestCollectPaths(t *testing.T) {
+	got := collectPaths([]string{"a", "b,c2,d3", "e4", "f,g"})
+	want := []string{"a", "b", "c2", "d3", "e4", "f", "g"}
+	if !cmp.Equal(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}