diff --git a/evogym/simulator/SimulatorCPP/Environment.cpp b/evogym/simulator/SimulatorCPP/Environment.cpp
index 5dee864e..42e77e0b 100644
--- a/evogym/simulator/SimulatorCPP/Environment.cpp
+++ b/evogym/simulator/SimulatorCPP/Environment.cpp
@@ -262,7 +262,7 @@ bool Environment::revert_to_snapshot(long int sim_time) {
 	return true;
 }
 
-Ref <MatrixXd> Environment::get_pos_at_time(long int sim_time) {
+RefMatrixXd Environment::get_pos_at_time(long int sim_time) {
 	
 	if (history.count(sim_time) <= 0) {
 		Matrix <double, 2, Dynamic> empty;
@@ -273,7 +273,7 @@ Ref <MatrixXd> Environment::get_pos_at_time(long int sim_time) {
 
 	return history[sim_time].points_pos;
 }
-Ref <MatrixXd> Environment::get_vel_at_time(long int sim_time) {
+RefMatrixXd Environment::get_vel_at_time(long int sim_time) {
 
 	if (history.count(sim_time) <= 0) {
 		Matrix <double, 2, Dynamic> empty;
@@ -285,7 +285,7 @@ Ref <MatrixXd> Environment::get_vel_at_time(long int sim_time) {
 	return history[sim_time].points_vel;
 }
 
-Ref <MatrixXd> Environment::object_pos_at_time(long int sim_time, string object_name) {
+RefMatrixXd Environment::object_pos_at_time(long int sim_time, string object_name) {
 
 	if (history.count(sim_time) <= 0 || object_name_to_index.count(object_name) <= 0) {
 		Matrix <double, 2, Dynamic> empty;
@@ -300,7 +300,7 @@ Ref <MatrixXd> Environment::object_pos_at_time(long int sim_time, string object_
 	return history[sim_time].points_pos(Eigen::all, Eigen::seq(min_index, max_index));
 
 }
-Ref <MatrixXd> Environment::object_vel_at_time(long int sim_time, string object_name) {
+RefMatrixXd Environment::object_vel_at_time(long int sim_time, string object_name) {
 
 	if (history.count(sim_time) <= 0 || object_name_to_index.count(object_name) <= 0) {
 		Matrix <double, 2, Dynamic> empty;
diff --git a/evogym/simulator/SimulatorCPP/Environment.h b/evogym/simulator/SimulatorCPP/Environment.h
index def4313f..b1b6302d 100644
--- a/evogym/simulator/SimulatorCPP/Environment.h
+++ b/evogym/simulator/SimulatorCPP/Environment.h
@@ -17,6 +17,12 @@
 using namespace std;
 using namespace Eigen;
 
+#ifdef __APPLE__
+using RefMatrixXd = Matrix <double, 2, Dynamic>;
+#else
+using RefMatrixXd = Ref <MatrixXd>;
+#endif
+
 class Environment
 {
 private:
@@ -92,11 +98,11 @@ class Environment
 	vector<SimObject*>* get_objects();
 	Robot* get_robot(string robot_name);
 
-	Ref <MatrixXd> get_pos_at_time(long int sim_time);
-	Ref <MatrixXd> get_vel_at_time(long int sim_time);
+	RefMatrixXd get_pos_at_time(long int sim_time);
+	RefMatrixXd get_vel_at_time(long int sim_time);
 
-	Ref <MatrixXd> object_pos_at_time(long int sim_time, string object_name);
-	Ref <MatrixXd> object_vel_at_time(long int sim_time, string object_name);
+	RefMatrixXd object_pos_at_time(long int sim_time, string object_name);
+	RefMatrixXd object_vel_at_time(long int sim_time, string object_name);
 	double object_orientation_at_time(long int sim_time, string object_name);
 	void translate_object(double x, double y, string object_name);
 
diff --git a/evogym/simulator/SimulatorCPP/Sim.cpp b/evogym/simulator/SimulatorCPP/Sim.cpp
index 935b7b7e..c00cd421 100644
--- a/evogym/simulator/SimulatorCPP/Sim.cpp
+++ b/evogym/simulator/SimulatorCPP/Sim.cpp
@@ -136,10 +136,10 @@ int Sim::get_time() {
 	return sim_time;
 }
 
-Ref <MatrixXd> Sim::pos_at_time(long int sim_time) {
+RefMatrixXd Sim::pos_at_time(long int sim_time) {
 	return environment.get_pos_at_time(sim_time);
 }
-Ref <MatrixXd> Sim::vel_at_time(long int sim_time) {
+RefMatrixXd Sim::vel_at_time(long int sim_time) {
 	return environment.get_vel_at_time(sim_time);
 }
 double Sim::object_orientation_at_time(long int sim_time, string object_name) {
@@ -151,10 +151,10 @@ void Sim::translate_object(double x, double y, string object_name) {
 }
 
 
-Ref <MatrixXd> Sim::object_pos_at_time(long int sim_time, string object_name) {
+RefMatrixXd Sim::object_pos_at_time(long int sim_time, string object_name) {
 	return environment.object_pos_at_time(sim_time, object_name);
 }
-Ref <MatrixXd> Sim::object_vel_at_time(long int sim_time, string object_name) {
+RefMatrixXd Sim::object_vel_at_time(long int sim_time, string object_name) {
 	return environment.object_vel_at_time(sim_time, object_name);
 }
 
diff --git a/evogym/simulator/SimulatorCPP/Sim.h b/evogym/simulator/SimulatorCPP/Sim.h
index 9d3eea8b..4b51406b 100644
--- a/evogym/simulator/SimulatorCPP/Sim.h
+++ b/evogym/simulator/SimulatorCPP/Sim.h
@@ -42,10 +42,10 @@ class Sim
 	void force_save();
 	void revert(long int sim_time);
 	int get_time();
-	Ref <MatrixXd> pos_at_time(long int sim_time);
-	Ref <MatrixXd> vel_at_time(long int sim_time);
-	Ref <MatrixXd> object_pos_at_time(long int sim_time, string object_name);
-	Ref <MatrixXd> object_vel_at_time(long int sim_time, string object_name);
+	RefMatrixXd pos_at_time(long int sim_time);
+	RefMatrixXd vel_at_time(long int sim_time);
+	RefMatrixXd object_pos_at_time(long int sim_time, string object_name);
+	RefMatrixXd object_vel_at_time(long int sim_time, string object_name);
 	double object_orientation_at_time(long int sim_time, string object_name);
 	void translate_object(double x, double y, string object_name);
 	Ref <MatrixXi> get_actuator_indices(string robot_name);