diff --git a/DDG4/src/Geant4Converter.cpp b/DDG4/src/Geant4Converter.cpp
index 3f95a7057def16cd0637491d0892088fca89074c..b8b86a216282c9ba0054610565d2fe0d8bec8e41 100644
--- a/DDG4/src/Geant4Converter.cpp
+++ b/DDG4/src/Geant4Converter.cpp
@@ -464,7 +464,7 @@ void* Geant4Converter::handleMaterial(const string& name, Material medium) const
       }
       int idx = -1;
       try   {
-        idx = tab->GetPropertyIndex(named->GetName());
+        idx = tab->GetConstPropertyIndex(named->GetName());
       }
       catch(const std::exception& e)   {
         exc_str = e.what();