diff --git a/src/blenderbim/blenderbim/tool/geometry.py b/src/blenderbim/blenderbim/tool/geometry.py
index 77c8c7eefb..3133115c62 100644
--- a/src/blenderbim/blenderbim/tool/geometry.py
+++ b/src/blenderbim/blenderbim/tool/geometry.py
@@ -470,8 +470,15 @@ class Geometry(blenderbim.core.tool.Geometry):
         usage_count = [0] * len(obj.material_slots)
         if not usage_count:  # if there are no materials, polygons will still use index 0
             return []
+
         for poly in obj.data.polygons:
             usage_count[poly.material_index] += 1
+
+        # remove usages for empty material slots
+        for i, slot in reversed(list(enumerate(obj.material_slots))):
+            if not slot.material:
+                del usage_count[i]
+
         styles = [style for style, usage in zip(styles, usage_count, strict=True) if usage > 0]
         return styles