diff --git a/src/utils/openmc/opencg_compatible.py b/src/utils/openmc/opencg_compatible.py
index 40d7b729e8..771ab9e835 100644
--- a/src/utils/openmc/opencg_compatible.py
+++ b/src/utils/openmc/opencg_compatible.py
@@ -830,6 +830,7 @@ def get_openmc_geometry(opencg_geometry):
     OPENMC_LATTICES.clear()
     OPENCG_LATTICES.clear()
 
+    opencg_geometry.assignAutoIds()
     opencg_root_universe = opencg_geometry._root_universe
     openmc_root_universe = get_openmc_universe(opencg_root_universe)