diff --git a/examples/openpilot/compile3.py b/examples/openpilot/compile3.py
index c8a4502a8f..cfdece7871 100644
--- a/examples/openpilot/compile3.py
+++ b/examples/openpilot/compile3.py
@@ -21,6 +21,8 @@ def compile(onnx_file):
   # TODO this seems dumb
   input_types = {k:(dtypes.float32 if v is dtypes.float16 else v) for k,v in input_types.items()}
   Tensor.manual_seed(100)
+  # replace symbolic dimensions (e.g. 'b' for dynamic batch) with 1
+  input_shapes = {k:tuple(s if isinstance(s, int) else 1 for s in shp) for k,shp in input_shapes.items()}
   inputs = {k:Tensor(Tensor.randn(*shp, dtype=input_types[k]).mul(8).realize().numpy(), device='NPY') for k,shp in sorted(input_shapes.items())}
   if not getenv("NPY_IMG"):
     inputs = {k:Tensor(v.numpy(), device=Device.DEFAULT).realize() if 'img' in k else v for k,v in inputs.items()}
diff --git a/tinygrad/nn/onnx.py b/tinygrad/nn/onnx.py
index 8850a525a5..ddab2db2f0 100644
--- a/tinygrad/nn/onnx.py
+++ b/tinygrad/nn/onnx.py
@@ -908,12 +908,13 @@ def get_onnx_ops() -> dict[str, types.FunctionType|dict[OpSetId, types.FunctionT
     return x * scale.reshape(1, -1, *[1] * (x.ndim-2)) + bias.reshape(1, -1, *[1] * (x.ndim-2))
   def InstanceNormalization(x:Tensor, scale:Tensor, bias:Tensor, epsilon:float=1e-05):
     return GroupNormalization(x, scale, bias, num_groups=cast(int, x.shape[1]), epsilon=epsilon)
-  def LayerNormalization(x:Tensor, scale:Tensor, bias:Tensor, axis:int=-1, epsilon:float=1e-05, stash_type:int=1):
+  def LayerNormalization(x:Tensor, scale:Tensor, bias:Tensor|None=None, axis:int=-1, epsilon:float=1e-05, stash_type:int=1):
     assert stash_type == 1, "only float32 is supported"
     axes = tuple(i for i in range(axis if axis >= 0 else x.ndim + axis, x.ndim))
     mean = (x32:=x.cast(dtypes.float)).mean(axis=axes, keepdim=True)
     inv_std_dev = (x32.sub(mean)).square().mean(axis=axes, keepdim=True).add(epsilon).rsqrt()
-    return (x32.sub(mean)*inv_std_dev).cast(x.dtype).mul(scale).add(bias), mean, inv_std_dev
+    ret = (x32.sub(mean)*inv_std_dev).cast(x.dtype).mul(scale)
+    return (ret.add(bias) if bias is not None else ret), mean, inv_std_dev
   def SkipLayerNormalization(x:Tensor, skip:Tensor, gamma:Tensor, beta:Tensor|None=None, bias:Tensor|None=None, epsilon:float=1e-12):
     x = x + skip
     if bias is not None: x = x + bias