diff --git a/cmd/modhex.go b/cmd/modhex.go
index 20ec8b8..b4c26bf 100644
--- a/cmd/modhex.go
+++ b/cmd/modhex.go
@@ -28,6 +28,11 @@ func main() {
 	}
 	flag.Parse()
 
+	if flag.NArg() < 1 {
+		flag.Usage()
+		os.Exit(0)
+	}
+
 	if decode {
 		// decode was selected