diff --git a/src/csg/csg.hpp b/src/csg/csg.hpp
index 7bce19472eeb6c2faef5594eb568050873080b8a..e29b857240b8ae461bd729c2501107525b8a7898 100644
--- a/src/csg/csg.hpp
+++ b/src/csg/csg.hpp
@@ -47,6 +47,7 @@ private:
   std::unique_ptr<Impl> m_pimpl;
 };
 
+std::shared_ptr<csg::Tree> get_csgtree_from_filename(std::string);
 std::unique_ptr<CsgIF> get_csgif_from_filename(std::string geom_file);
 
 } // namespace csg
diff --git a/src/csg/impl/csg.cpp b/src/csg/impl/csg.cpp
index 7ea6c38ee30693a6c0321b2bea4b36fda775f0eb..99b104ba0fd7dc2e039b323388de34f55f955432 100644
--- a/src/csg/impl/csg.cpp
+++ b/src/csg/impl/csg.cpp
@@ -54,14 +54,17 @@ double CsgIF::operator()(double xx, double yy, double zz) const noexcept {
   return m_pimpl->call_signed_distance(m_state, xx, yy, zz);
 }
 
-std::unique_ptr<CsgIF> get_csgif_from_filename(std::string geom_file) {
-
+std::shared_ptr<csg::Tree> get_csgtree_from_filename(std::string geom_file) {
   auto csg_str = read_csg(geom_file);
   if (!csg_str) {
     std::cout << "Unable to read .csg file:  " << geom_file << std::endl;
     return nullptr;
   }
-  auto csg_obj = csg::parse_csg(csg_str.value());
+  return csg::parse_csg(csg_str.value());
+}
+
+std::unique_ptr<CsgIF> get_csgif_from_filename(std::string geom_file) {
+  auto csg_obj = get_csgtree_from_filename(geom_file);
 
   if (!csg_obj) {
     std::cout << "Failed to parse .csg file:  " << geom_file << std::endl;
diff --git a/src/inputs/geometry.cpp b/src/inputs/geometry.cpp
index 10d723db361e324c534f73fcd787483555ab63ab..7f48246fcd61d18bc782c78ec0346015319ff010 100644
--- a/src/inputs/geometry.cpp
+++ b/src/inputs/geometry.cpp
@@ -6,6 +6,17 @@ namespace solver {
 
 std::optional<solver::GeometrySettings> make_geometry(solver::InputInfo ii) {
   solver::GeometrySettings geo;
+
+  if (!ii.count(CSG_FILENAME)) {
+    require(CSG_FILENAME);
+    return std::nullopt;
+  }
+  auto csg_filename = std::get<solver::StringArray>(ii[CSG_FILENAME]);
+  if (csg_filename.size() != 1) {
+    std::cout << CSG_FILENAME << " should only have 1 element" << std::endl;
+    return std::nullopt;
+  }
+
   if (!ii.count(PROB_LO)) {
     require(PROB_LO);
     return std::nullopt;
@@ -34,6 +45,7 @@ std::optional<solver::GeometrySettings> make_geometry(solver::InputInfo ii) {
     return std::nullopt;
   }
 
+  geo.csg_filename = csg_filename[0];
   std::get<0>(geo.axes).high = highs[0];
   std::get<0>(geo.axes).low = lows[0];
   std::get<0>(geo.axes).periodic = is_periodic[0];
diff --git a/src/inputs/inputs.hpp b/src/inputs/inputs.hpp
index 79595037d5f1eae60acf2c369e31babd88dca3d5..7129f67e799bd12e8aa6bcf91fb16e4656b92037 100644
--- a/src/inputs/inputs.hpp
+++ b/src/inputs/inputs.hpp
@@ -7,6 +7,7 @@ static const std::string DT_MIN("mfix.dt_min");
 static const std::string PERIODIC("geometry.is_periodic");
 static const std::string PROB_HI("geometry.prob_hi");
 static const std::string PROB_LO("geometry.prob_lo");
+static const std::string CSG_FILENAME("mfix.geometry_filename");
 
 // Mesh
 static const std::string BLOCKING_FACTOR("amr.blocking_factor");
diff --git a/src/inputs/solver.hpp b/src/inputs/solver.hpp
index 868f5157a69e4674db24a088a646f5527b700bfe..8136360a5354d92c8b33eac5edba343b0274c104 100644
--- a/src/inputs/solver.hpp
+++ b/src/inputs/solver.hpp
@@ -26,6 +26,7 @@ struct GeometryAxis {
 };
 struct GeometrySettings {
   std::array<GeometryAxis, 3> axes;
+  std::string csg_filename;
 };
 
 struct MeshAxis {
diff --git a/src/inputs/tests/solver.t.cpp b/src/inputs/tests/solver.t.cpp
index d26a67ed6ccd423e5c739f776bd9c7a16a52b02c..f160a05d8a3498ea5e2a5a18268e1b34d65490f4 100644
--- a/src/inputs/tests/solver.t.cpp
+++ b/src/inputs/tests/solver.t.cpp
@@ -18,6 +18,7 @@ TEST_CASE("from_origin", "[]") {
   ii[PROB_LO] = std::vector<double>({-4, -5, -6});
   ii[PROB_HI] = solver::NumberArray({0.004, 0.001, 0.001});
   ii[PERIODIC] = solver::NumberArray({0, 0, 0});
+  ii[CSG_FILENAME] = solver::StringArray({"geometry.csg",});
 
   // Mesh
   ii[N_CELL] = solver::NumberArray({11, 22, 33});