diff --git a/core/src/main/java/org/matsim/alonso_mora/algorithm/assignment/MpsAssignmentWriter.java b/core/src/main/java/org/matsim/alonso_mora/algorithm/assignment/MpsAssignmentWriter.java
index 8572fae..e56cceb 100644
--- a/core/src/main/java/org/matsim/alonso_mora/algorithm/assignment/MpsAssignmentWriter.java
+++ b/core/src/main/java/org/matsim/alonso_mora/algorithm/assignment/MpsAssignmentWriter.java
@@ -7,6 +7,7 @@
 import java.io.OutputStreamWriter;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.Collectors;
 
 import org.matsim.alonso_mora.algorithm.AlonsoMoraRequest;
@@ -48,18 +49,18 @@ public void write(File path) throws IOException {
 
 		int rowIndex = 0;
 
-		writer.write(String.format(" N R%07d\n", rowIndex));
+		writer.write(String.format(Locale.US, " N R%07d\n", rowIndex));
 		rowIndex++;
 
 		// <= 1 rows for the vehicles
 		for (int i = 0; i < numberOfVehicles; i++) {
-			writer.write(String.format(" L R%07d\n", rowIndex));
+			writer.write(String.format(Locale.US, " L R%07d\n", rowIndex));
 			rowIndex++;
 		}
 
 		// == 1 rows for the requests
 		for (int i = 0; i < numberOfRequests; i++) {
-			writer.write(String.format(" E R%07d\n", rowIndex));
+			writer.write(String.format(Locale.US, " E R%07d\n", rowIndex));
 			rowIndex++;
 		}
 
@@ -69,40 +70,40 @@ public void write(File path) throws IOException {
 		// Trip influences
 		for (int i = 0; i < numberOfTrips; i++) {
 			AlonsoMoraTrip trip = tripList.get(i);
-			writer.write(String.format(" T%d R%07d %f\n", i, 0, trip.getResult().getCost()));
+			writer.write(String.format(Locale.US, " T%d R%07d %f\n", i, 0, trip.getResult().getCost()));
 
 			int vehicleIndex = vehicleList.indexOf(trip.getVehicle());
-			writer.write(String.format(" T%d R%07d 1\n", i, vehicleIndex + 1));
+			writer.write(String.format(Locale.US, " T%d R%07d 1\n", i, vehicleIndex + 1));
 
 			for (AlonsoMoraRequest request : trip.getRequests()) {
 				int requestIndex = requestList.indexOf(request);
-				writer.write(String.format(" T%d R%07d 1\n", i, requestIndex + numberOfVehicles + 1));
+				writer.write(String.format(Locale.US, " T%d R%07d 1\n", i, requestIndex + numberOfVehicles + 1));
 			}
 		}
 
 		// Request influences
 		for (int i = 0; i < numberOfRequests; i++) {
 			double penalty = requestList.get(i).isAssigned() ? unassignmentPenalty : rejectionPenalty;
-			writer.write(String.format(" x%d R%07d %f R%07d 1\n", i, 0, penalty, i + numberOfVehicles + 1));
+			writer.write(String.format(Locale.US, " x%d R%07d %f R%07d 1\n", i, 0, penalty, i + numberOfVehicles + 1));
 		}
 
 		writer.write(" M0000002 'MARKER' 'INTEND'\n");
 		writer.write("RHS\n");
 
 		for (int i = 0; i < numberOfVehicles + numberOfRequests; i++) {
-			writer.write(String.format(" RHS1 R%07d 1\n", i + 1));
+			writer.write(String.format(Locale.US, " RHS1 R%07d 1\n", i + 1));
 		}
 
 		writer.write("BOUNDS\n");
 
 		// Trip variables bounds
 		for (int i = 0; i < numberOfTrips; i++) {
-			writer.write(String.format(" UP BND1 T%d 1\n", i));
+			writer.write(String.format(Locale.US, " UP BND1 T%d 1\n", i));
 		}
 
 		// Trip variables bounds
 		for (int i = 0; i < numberOfRequests; i++) {
-			writer.write(String.format(" UP BND1 x%d 1\n", i));
+			writer.write(String.format(Locale.US, " UP BND1 x%d 1\n", i));
 		}
 
 		writer.write("ENDATA\n");
diff --git a/core/src/main/java/org/matsim/alonso_mora/algorithm/relocation/MpsRelocationWriter.java b/core/src/main/java/org/matsim/alonso_mora/algorithm/relocation/MpsRelocationWriter.java
index 493f8e3..9091e61 100644
--- a/core/src/main/java/org/matsim/alonso_mora/algorithm/relocation/MpsRelocationWriter.java
+++ b/core/src/main/java/org/matsim/alonso_mora/algorithm/relocation/MpsRelocationWriter.java
@@ -6,6 +6,7 @@
 import java.io.IOException;
 import java.io.OutputStreamWriter;
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.Collectors;
 
 import org.matsim.alonso_mora.algorithm.relocation.RelocationSolver.Relocation;
@@ -36,10 +37,10 @@ public void write(File path) throws IOException {
 		writer.write("ROWS\n");
 
 		// Objective
-		writer.write(String.format(" N R%07d\n", 0));
+		writer.write(String.format(Locale.US, " N R%07d\n", 0));
 
 		// Constraint (equality)
-		writer.write(String.format(" E R%07d\n", 1));
+		writer.write(String.format(Locale.US, " E R%07d\n", 1));
 
 		writer.write("COLUMNS\n");
 		writer.write(" M0000001 'MARKER' 'INTORG'\n");
@@ -47,21 +48,21 @@ public void write(File path) throws IOException {
 		for (int i = 0; i < numberOfVariables; i++) {
 			// Objective
 			Relocation relocation = relocations.get(i);
-			writer.write(String.format(" T%d R%07d %f", i, 0, relocation.cost));
+			writer.write(String.format(Locale.US, " T%d R%07d %f", i, 0, relocation.cost));
 
 			// Constraint
-			writer.write(String.format(" R%07d 1\n", 1));
+			writer.write(String.format(Locale.US, " R%07d 1\n", 1));
 		}
 
 		writer.write(" M0000002 'MARKER' 'INTEND'\n");
 		writer.write("RHS\n");
-		writer.write(String.format(" RHS1 R%07d %d\n", 1, numberOfAssignments));
+		writer.write(String.format(Locale.US, " RHS1 R%07d %d\n", 1, numberOfAssignments));
 
 		writer.write("BOUNDS\n");
 
 		for (int i = 0; i < numberOfVariables; i++) {
-			writer.write(String.format(" UP BND1 T%d 1\n", i));
-			writer.write(String.format(" LO BND1 T%d 0\n", i));
+			writer.write(String.format(Locale.US, " UP BND1 T%d 1\n", i));
+			writer.write(String.format(Locale.US, " LO BND1 T%d 0\n", i));
 		}
 
 		writer.write("ENDATA\n");