diff --git a/auto_transformers.py b/auto_transformers.py
index 0a601a2..496f989 100644
--- a/auto_transformers.py
+++ b/auto_transformers.py
@@ -212,7 +212,8 @@ class AutoTransformers(NNOperator):
                 input_names=list(self.onnx_config['inputs'].keys()),
                 output_names=list(self.onnx_config['outputs'].keys()),
                 dynamic_axes=dynamic_axes,
-                opset_version=torch.onnx.constant_folding_opset_versions[-1],
+                opset_version=torch.onnx.constant_folding_opset_versions[-1] if hasattr(
+                    torch.onnx, 'constant_folding_opset_versions') else 14,
                 do_constant_folding=True,
             )
         # todo: elif format == 'tensorrt':