diff --git a/io_scene_obj/export_obj.py b/io_scene_obj/export_obj.py
index 1bb41ebff3480149832d7a2ee84538a995abc6b1..a0926cc47f3f1b1216be237998966014dfc4d5d3 100644
--- a/io_scene_obj/export_obj.py
+++ b/io_scene_obj/export_obj.py
@@ -393,7 +393,7 @@ def write_file(filepath, objects, scene,
             # avoid bad index errors
             if not materials:
                 materials = [None]
-                material_names = [""]
+                material_names = [name_compat(None)]
 
             # Sort by Material, then images
             # so we dont over context switch in the obj file.