diff --git a/cmd/pkgproto/main.go b/cmd/pkgproto/main.go
index a536f67..cbd0c65 100644
--- a/cmd/pkgproto/main.go
+++ b/cmd/pkgproto/main.go
@@ -116,4 +116,5 @@ func usage() {
 	fmt.Fprintf(os.Stderr,
 		"usage: %s [-i] [-c class] [path ...]\n",
 			progname)
+	os.Exit(1)
 }