diff --git a/src/Init/GridInit.cpp b/src/Init/GridInit.cpp
index 65d788eea..dcd28db75 100644
--- a/src/Init/GridInit.cpp
+++ b/src/Init/GridInit.cpp
@@ -4,8 +4,6 @@
 #include <RInside.h>
 #include <Rcpp/Function.h>
 #include <Rcpp/vector/instantiation.h>
-#include <algorithm>
-#include <cstdint>
 #include <map>
 #include <regex>
 #include <string>
@@ -77,8 +75,10 @@ getModuleSizes(IPhreeqcPOET &phreeqc, const Rcpp::List &initial_grid) {
 
 void InitialList::initGrid(const Rcpp::List &grid_input) {
   // parse input values
-  const std::string script = Rcpp::as<std::string>(grid_input["pqc_in"]);
-  const std::string database = Rcpp::as<std::string>(grid_input["pqc_db"]);
+  const std::string script = Rcpp::as<std::string>(
+      grid_input[getGridMemberString(GridMembers::PQC_SCRIPT_FILE)]);
+  const std::string database = Rcpp::as<std::string>(
+      grid_input[getGridMemberString(GridMembers::PQC_DB_FILE)]);
 
   std::string script_rp(PATH_MAX, '\0');
   std::string database_rp(PATH_MAX, '\0');
@@ -93,8 +93,10 @@ void InitialList::initGrid(const Rcpp::List &grid_input) {
                              database);
   }
 
-  Rcpp::NumericMatrix grid_def = grid_input["grid_def"];
-  Rcpp::NumericVector grid_size = grid_input["grid_size"];
+  Rcpp::NumericMatrix grid_def =
+      grid_input[getGridMemberString(GridMembers::GRID_DEF)];
+  Rcpp::NumericVector grid_size =
+      grid_input[getGridMemberString(GridMembers::GRID_SIZE)];
   // Rcpp::NumericVector constant_cells = grid["constant_cells"].;
 
   this->n_rows = grid_def.nrow();
diff --git a/src/Init/InitialList.cpp b/src/Init/InitialList.cpp
index d37fee1fc..a433097a2 100644
--- a/src/Init/InitialList.cpp
+++ b/src/Init/InitialList.cpp
@@ -2,7 +2,7 @@
 
 namespace poet {
 void InitialList::initializeFromList(const Rcpp::List &setup) {
-  initGrid(setup["grid"]);
-  initDiffusion(setup["diffusion"]);
+  initGrid(setup[grid_key]);
+  initDiffusion(setup[diffusion_key]);
 }
 } // namespace poet
\ No newline at end of file
diff --git a/src/Init/InitialList.hpp b/src/Init/InitialList.hpp
index 30289c252..b75a9b2d8 100644
--- a/src/Init/InitialList.hpp
+++ b/src/Init/InitialList.hpp
@@ -3,9 +3,12 @@
 #include <RInside.h>
 #include <Rcpp.h>
 #include <Rcpp/vector/instantiation.h>
+#include <array>
+#include <cstddef>
 #include <cstdint>
 
 #include <IPhreeqcPOET.hpp>
+#include <map>
 #include <utility>
 #include <vector>
 
@@ -26,6 +29,32 @@ private:
   RInside &R;
 
   // Grid members
+  static constexpr const char *grid_key = "Grid";
+
+  enum class GridMembers {
+    PQC_SCRIPT_STRING,
+    PQC_SCRIPT_FILE,
+    PQC_DB_STRING,
+    PQC_DB_FILE,
+    GRID_DEF,
+    GRID_SIZE,
+    CONSTANT_CELLS,
+    POROSITY,
+    ENUM_SIZE
+  };
+
+  static constexpr std::size_t size_GridMembers =
+      static_cast<std::size_t>(InitialList::GridMembers::ENUM_SIZE);
+
+  static constexpr std::array<const char *, size_GridMembers>
+      GridMembersString = {"pqc_in_string",  "pqc_in_file", "pqc_db_string",
+                           "pqc_db_file",    "grid_def",    "grid_size",
+                           "constant_cells", "porosity"};
+
+  constexpr const char *getGridMemberString(GridMembers member) const {
+    return GridMembersString[static_cast<std::size_t>(member)];
+  }
+
   void initGrid(const Rcpp::List &grid_input);
   std::uint8_t dim;
 
@@ -49,6 +78,9 @@ private:
   IPhreeqcPOET::ModulesArray module_sizes;
 
   // Diffusion members
+
+  static constexpr const char *diffusion_key = "Diffusion";
+
   void initDiffusion(const Rcpp::List &diffusion_input);
   Rcpp::List boundaries;