diff --git a/pixal3d_mlx/mesh.py b/pixal3d_mlx/mesh.py
index 52d653a..fc51200 100644
--- a/pixal3d_mlx/mesh.py
+++ b/pixal3d_mlx/mesh.py
@@ -28,6 +28,16 @@ import numpy as np
 # Upstream fixes both: the model always works in a unit cube centred on the origin.
 AABB = [[-0.5, -0.5, -0.5], [0.5, 0.5, 0.5]]
 
+# How the texture decoder's 6 channels map to PBR slots (pipeline's pbr_attr_layout).
+# o_voxel indexes this dict by name and raises KeyError on any missing slot, so a
+# partial layout fails deep inside the baker rather than at the call.
+PBR_ATTR_LAYOUT = {
+    "base_color": slice(0, 3),
+    "metallic": slice(3, 4),
+    "roughness": slice(4, 5),
+    "alpha": slice(5, 6),
+}
+
 
 def _torch(a):
     import torch