diff --git a/ChemistryLib/ChemicalSolverInterface.h b/ChemistryLib/ChemicalSolverInterface.h
index 96cf73c504b70953bda1e76b198ab2e834ded3c3..ed55c782aad66a923289a042046f812093608b44 100644
--- a/ChemistryLib/ChemicalSolverInterface.h
+++ b/ChemistryLib/ChemicalSolverInterface.h
@@ -29,5 +29,8 @@ public:
     }
 
     virtual ~ChemicalSolverInterface() = default;
+
+public:
+    std::vector<std::vector<GlobalIndexType>> chemical_system_index_map;
 };
 }  // namespace ChemistryLib