diff --git a/python/py_aka_parser.cc b/python/py_aka_parser.cc
index e49650376..83131a7b4 100644
--- a/python/py_aka_parser.cc
+++ b/python/py_aka_parser.cc
@@ -1,69 +1,72 @@
 /* -------------------------------------------------------------------------- */
 #include "py_aka_array.hh"
 /* -------------------------------------------------------------------------- */
 #include <aka_common.hh>
 #include <parameter_registry.hh>
 #include <parsable.hh>
 #include <parser.hh>
 /* -------------------------------------------------------------------------- */
 #include <map>
 #include <pybind11/operators.h>
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 /* -------------------------------------------------------------------------- */
 namespace py = pybind11;
 /* -------------------------------------------------------------------------- */
 
 namespace akantu {
 std::map<void *, std::map<std::string, void *>> map_params;
 
 __attribute__((visibility("default"))) void register_parser(py::module & mod) {
 
   py::enum_<ParameterAccessType>(mod, "ParameterAccessType", py::arithmetic())
       .value("_pat_internal", _pat_internal)
       .value("_pat_writable", _pat_writable)
       .value("_pat_readable", _pat_readable)
       .value("_pat_modifiable", _pat_modifiable)
       .value("_pat_parsable", _pat_parsable)
       .value("_pat_parsmod", _pat_parsmod)
       .export_values();
 
   py::class_<ParameterRegistry>(mod, "ParameterRegistry",
                                 py::multiple_inheritance())
       .def("registerParamReal",
            [](ParameterRegistry & self, const std::string & name, UInt type,
               const std::string & description) {
              Real * p = new Real;
              map_params[&self][name] = p;
              self.registerParam<Real>(name, *p, ParameterAccessType(type),
                                       description);
            })
       .def("registerParamReal",
            [](ParameterRegistry & self, const Real & _default,
               const std::string & name, UInt type,
               const std::string & description) {
              Real * p = new Real;
              map_params[&self][name] = p;
              self.registerParam<Real>(name, *p, _default,
                                       ParameterAccessType(type), description);
            })
       .def("getReal",
            [](ParameterRegistry & self, const std::string & name) {
              return Real(self.get(name));
            })
-      .def("getMatrix", [](ParameterRegistry & self, const std::string & name) {
-        Matrix<Real> res = self.get(name);
-        return res;
-      });
+      .def("getMatrix",
+           [](ParameterRegistry & self, const std::string & name) {
+             const Matrix<Real> & res =
+                 static_cast<const Matrix<Real> &>(self.get(name));
+             return res;
+           },
+           py::return_value_policy::copy);
 
   py::class_<Parsable, ParameterRegistry>(mod, "Parsable",
                                           py::multiple_inheritance())
       .def(py::init<const ParserType &, const ID &>());
 
   mod.def("parseInput",
           [](const std::string & input_file) {
             getStaticParser().parse(input_file);
           },
           "Parse an Akantu input file");
 }
 } // namespace akantu