diff --git a/egs/ljspeech/TTS/vits/export-onnx.py b/egs/ljspeech/TTS/vits/export-onnx.py
index ecf5341e3..f82f9dbe9 100755
--- a/egs/ljspeech/TTS/vits/export-onnx.py
+++ b/egs/ljspeech/TTS/vits/export-onnx.py
@@ -166,6 +166,8 @@ def export_model_onnx(
         The VITS generator.
       model_filename:
         The filename to save the exported ONNX model.
+      vocab_size:
+        Number of tokens used in training.
       opset_version:
         The opset version to use.
     """