diff --git a/jaxonnxruntime/onnx_ops/flatten.py b/jaxonnxruntime/onnx_ops/flatten.py
index ca644b8..f777392 100644
--- a/jaxonnxruntime/onnx_ops/flatten.py
+++ b/jaxonnxruntime/onnx_ops/flatten.py
@@ -51,6 +51,14 @@ def version_1(
     cls._prepare(node, inputs, onnx_flatten)
     return onnx_flatten
 
+  @classmethod
+  def version_9(
+      cls, node: onnx_node.OnnxNode, inputs: Sequence[Any]
+  ) -> Callable[..., Any]:
+    """ONNX version_9 Flatten op."""
+    cls._prepare(node, inputs, onnx_flatten)
+    return onnx_flatten
+
   @classmethod
   def version_11(
       cls, node: onnx_node.OnnxNode, inputs: Sequence[Any]