diff --git a/mytools/generateMock.cpp b/mytools/generateMock.cpp
index 93c5f71..2d36ed8 100644
--- a/mytools/generateMock.cpp
+++ b/mytools/generateMock.cpp
@@ -100,7 +100,7 @@ Interpolate make_cosmological_redshift(double OM, double OL, double z0, double z
   return buildFromVector(pairs);
 }
 
-void metricTransform(SimuData *data, int axis)
+void metricTransform(SimuData *data, int axis, bool reshift)
 {
   int x0, x1, x2;
 
@@ -121,6 +121,7 @@ void metricTransform(SimuData *data, int axis)
   Interpolate z_vs_D = make_cosmological_redshift(data->Omega_M, data->Omega_Lambda, 0., 2.0); // Redshift 2 should be sufficient ?
     
   double z0 = 1/data->time - 1;
+  double z_base = reshift ? z0 : 0;
   TotalExpansion e_computer;
   double baseComovingDistance;
 
@@ -141,7 +142,7 @@ void metricTransform(SimuData *data, int axis)
       double reduced_red = (z + baseComovingDistance)*100./LIGHT_SPEED;
 
       // Distorted redshift
-      z = z_vs_D.compute(reduced_red)*LIGHT_SPEED/100.;
+      z = (z_vs_D.compute(reduced_red)-z_base)*LIGHT_SPEED/100.;
       // Add peculiar velocity
       z += v/100;
     }
@@ -320,7 +321,7 @@ int main(int argc, char **argv)
   cout << "Omega_M = " << simu->Omega_M << endl;
   cout << "Omega_Lambda = " << simu->Omega_Lambda << endl;
 
-  metricTransform(simu, args_info.axis_arg);
+  metricTransform(simu, args_info.axis_arg, args_info.preReShift_flag);
 
   makeBox(simu, simuOut, args_info);
   delete simu;
diff --git a/mytools/generateMock.ggo b/mytools/generateMock.ggo
index 67d8e8f..a581ef2 100644
--- a/mytools/generateMock.ggo
+++ b/mytools/generateMock.ggo
@@ -17,4 +17,6 @@ option "rangeX_max"   -   "Maximum range in X for making the box" double require
 option "rangeY_min"   -   "Minimum range in Y for making the box" double required
 option "rangeY_max"   -   "Maximum range in Y for making the box" double required
 option "rangeZ_min"   -   "Minimum range in Z for making the box (after distortion)" double required
-option "rangeZ_max"   -   "Maximum range in Z for making the box (after distortion)" double required
\ No newline at end of file
+option "rangeZ_max"   -   "Maximum range in Z for making the box (after distortion)" double required
+
+option "preReShift" - "Reshift the zero of the Z axis" flag off
\ No newline at end of file