diff --git a/computer_aided_design_for_optical_instruments/segmented_mirror/__init__.py b/computer_aided_design_for_optical_instruments/segmented_mirror/__init__.py
index 3ebcffd..af913fa 100644
--- a/computer_aided_design_for_optical_instruments/segmented_mirror/__init__.py
+++ b/computer_aided_design_for_optical_instruments/segmented_mirror/__init__.py
@@ -144,6 +144,7 @@ def add_to_frame(
 
     # facet
     # -----
+    pp = posixpath
     assert facet_id_start >= 0
     facet_outer_radius = facet_inner_hex_radius * (2.0 / np.sqrt(3.0))
     facet_curvature_radius = 2.0 * focal_length
@@ -157,9 +158,9 @@ def add_to_frame(
         ref="facet",
     )
     facet_mtl_to_boundary_layers_map = {
-        "facet/front": boundary_layer_facet_front,
-        "facet/back": boundary_layer_facet_body,
-        "facet/side": boundary_layer_facet_body,
+        pp.join("facet", "front"): pp.join(ref, boundary_layer_facet_front),
+        pp.join("facet", "back"): pp.join(ref, boundary_layer_facet_body),
+        pp.join("facet", "side"): pp.join(ref, boundary_layer_facet_body),
     }
 
     objs = {}
diff --git a/computer_aided_design_for_optical_instruments/version.py b/computer_aided_design_for_optical_instruments/version.py
index 3b93d0b..27fdca4 100644
--- a/computer_aided_design_for_optical_instruments/version.py
+++ b/computer_aided_design_for_optical_instruments/version.py
@@ -1 +1 @@
-__version__ = "0.0.2"
+__version__ = "0.0.3"