diff --git a/onnxscript/function_libs/torch_lib/ops/core.py b/onnxscript/function_libs/torch_lib/ops/core.py
index 971f63902..abdd91f03 100644
--- a/onnxscript/function_libs/torch_lib/ops/core.py
+++ b/onnxscript/function_libs/torch_lib/ops/core.py
@@ -8432,16 +8432,16 @@ def aten_unbind(self: TTensor, dim: int = 0) -> Sequence[TTensor]:
     return op.SplitToSequence(self, split_sizes, axis=dim, keepdims=False)
 
 
-@torch_op("aten::unflatten.int")
-def aten_unflatten(self: TReal, dim: INT64, sizes: INT64):
+@torch_op("aten::unflatten.int", trace_only=True)
+def aten_unflatten(self: TReal, dim: int, sizes: Sequence[INT64]):
     """unflatten(Tensor(a) self, int dim, SymInt[] sizes) -> Tensor(a)"""
 
     self_size = op.Shape(self)
 
     # PyTorch accepts negative dim as reversed counting
-    self_rank = op.Size(self_size)
-    dim = self_rank + dim
-    dim = dim % self_rank
+    self_rank = len(self.shape)
+    if dim < 0:
+        dim = self_rank + dim
 
     head_start_idx = op.Constant(value_ints=[0])
     head_end_idx = op.Reshape(dim, op.Constant(value_ints=[1]))
@@ -8451,8 +8451,16 @@ def aten_unflatten(self: TReal, dim: INT64, sizes: INT64):
     tail_end_idx = op.Constant(value_ints=[_INT64_MAX])
     tail_part_rank = op.Slice(self_size, tail_start_idx, tail_end_idx)
 
-    final_shape = op.Concat(head_part_rank, sizes, tail_part_rank, axis=0)
+    sizes = [op.Reshape(size, op.Constant(value_ints=[1])) for size in sizes]
 
+    # corner case 1: head part is None
+    if dim == 0:
+        final_shape = op.Concat(*sizes, tail_part_rank, axis=0)
+    # corner case 2: tail part is None
+    elif dim == self_rank - 1:
+        final_shape = op.Concat(head_part_rank, *sizes, axis=0)
+    else:
+        final_shape = op.Concat(head_part_rank, *sizes, tail_part_rank, axis=0)
     return op.Reshape(self, final_shape)
 
 
diff --git a/tests/function_libs/torch_lib/ops_test_data.py b/tests/function_libs/torch_lib/ops_test_data.py
index c6b52be0c..c1d380f9f 100644
--- a/tests/function_libs/torch_lib/ops_test_data.py
+++ b/tests/function_libs/torch_lib/ops_test_data.py
@@ -429,13 +429,6 @@ def _sum_input_wrangler(
     return args, kwargs
 
 
-def _unflatten_input_wrangler(
-    args: list[Any], kwargs: dict[str, Any]
-) -> tuple[list[Any], dict[str, Any]]:
-    args[1] = np.array(args[1], dtype=np.int64)
-    return args, kwargs
-
-
 def _where_input_wrangler(
     args: list[Any], kwargs: dict[str, Any]
 ) -> tuple[list[Any], dict[str, Any]]:
@@ -1471,14 +1464,9 @@ def _where_input_wrangler(
     TorchLibOpInfo(
         "unflatten",
         core_ops.aten_unflatten,
-        input_wrangler=_unflatten_input_wrangler,
-    )
-    .xfail(
+    ).xfail(
         matcher=lambda sample: any(dim == 0 for dim in sample.input.shape),
         reason="fixme: Logic not implemented for size 0 inputs in op.Reshape",
-    )
-    .xfail(
-        reason="fixme: https://github.com/pytorch/pytorch/issues/146336",
     ),
     TorchLibOpInfo("unfold", core_ops.aten_unfold),
     TorchLibOpInfo("ops.aten.unfold", core_ops.aten_unfold),