diff --git a/documentation/release_6.3.htm b/documentation/release_6.3.htm
index bdcc5dce7..b15a601cd 100644
--- a/documentation/release_6.3.htm
+++ b/documentation/release_6.3.htm
@@ -48,6 +48,10 @@ <h3>New functionality</h3>
   <li>
     <tt>stir_timings</tt> has now an extra option to parse a par-file for a projector-pair.
   </li>
+  <li>
+    Added the ability to set a forward projector for mask projection in the <code>ScatterEstimation</code> class.<br>
+    <a href=https://github.com/UCL/STIR/pull/1530>PR #1530</a>
+  </li>
   <li>
     Duration in sinogram interfile/exam_info obtained from <tt>lm_to_projdata</tt> has the correct value if we unlist all the events. This is not true for ROOT files<br>
     <a href=https://github.com/UCL/STIR/pull/1519>PR #1519</a>
diff --git a/src/include/stir/scatter/ScatterEstimation.h b/src/include/stir/scatter/ScatterEstimation.h
index e3ed9a722..84d91e745 100644
--- a/src/include/stir/scatter/ScatterEstimation.h
+++ b/src/include/stir/scatter/ScatterEstimation.h
@@ -39,6 +39,7 @@
 
 #include "stir/stir_math.h"
 #include "stir/FilePath.h"
+#include "stir/recon_buildblock/ForwardProjectorByBin.h"
 
 START_NAMESPACE_STIR
 
@@ -171,6 +172,11 @@ class ScatterEstimation : public ParsingObject
   void set_recompute_mask_image(bool arg);
   void set_recompute_mask_projdata(bool arg);
 
+  //! Sets the forward projector for the scatter estimation
+  void set_forward_projector_for_mask_sptr(const shared_ptr<ForwardProjectorByBin> projector_sptr);
+  //! Get the forward projector used for the scatter estimation mask calculation
+  shared_ptr<ForwardProjectorByBin> get_forward_projector_for_mask_sptr() const;
+
   inline void set_scatter_simulation_method_sptr(const shared_ptr<ScatterSimulation>);
 
   inline void set_num_iterations(int);
@@ -276,6 +282,8 @@ class ScatterEstimation : public ParsingObject
   //! The file name for the attenuation coefficients.
   //! If they are to be recalculated they will be stored here, if set.
   std::string atten_coeff_filename;
+  //! ForwardProjector
+  shared_ptr<ForwardProjectorByBin> forward_projector_for_mask_sptr;
 
   //! \details the set of parameters to obtain a mask from the attenuation image
   /*! The attenuation image will be thresholded to find a plausible mask for where there
diff --git a/src/scatter_buildblock/ScatterEstimation.cxx b/src/scatter_buildblock/ScatterEstimation.cxx
index efe3e2d9b..54cf56167 100644
--- a/src/scatter_buildblock/ScatterEstimation.cxx
+++ b/src/scatter_buildblock/ScatterEstimation.cxx
@@ -112,6 +112,10 @@ ScatterEstimation::initialise_keymap()
   this->parser.add_key("mask projdata filename", &this->mask_projdata_filename);
   this->parser.add_key("tail fitting parameter filename", &this->tail_mask_par_filename);
   // END MASK
+
+  // Forward projector for mask projection
+  this->parser.add_parsing_key("forward projector for mask type", &this->forward_projector_for_mask_sptr);
+
   this->parser.add_key("background projdata filename", &this->back_projdata_filename);
   this->parser.add_parsing_key("Normalisation type", &this->norm_3d_sptr);
   this->parser.add_key("attenuation correction factors filename", &this->atten_coeff_filename);
@@ -451,6 +455,18 @@ ScatterEstimation::set_recompute_mask_projdata(bool arg)
   this->recompute_mask_projdata = arg;
 }
 
+void
+ScatterEstimation::set_forward_projector_for_mask_sptr(const shared_ptr<ForwardProjectorByBin> projector_sptr)
+{
+  this->forward_projector_for_mask_sptr = projector_sptr;
+}
+
+shared_ptr<ForwardProjectorByBin>
+ScatterEstimation::get_forward_projector_for_mask_sptr() const
+{
+  return forward_projector_for_mask_sptr;
+}
+
 bool
 ScatterEstimation::already_setup() const
 {
@@ -1237,30 +1253,32 @@ ScatterEstimation::project_mask_image()
         }
     }
 
-  shared_ptr<ForwardProjectorByBin> forw_projector_sptr;
-  shared_ptr<ProjMatrixByBin> PM(new ProjMatrixByBinUsingRayTracing());
-  forw_projector_sptr.reset(new ForwardProjectorByBinUsingProjMatrixByBin(PM));
+  if (!this->forward_projector_for_mask_sptr)
+    {
+      shared_ptr<ProjMatrixByBin> PM(new ProjMatrixByBinUsingRayTracing());
+      forward_projector_for_mask_sptr.reset(new ForwardProjectorByBinUsingProjMatrixByBin(PM));
+    }
   info(boost::format("ScatterEstimation: Forward projector used for the calculation of "
                      "the tail mask: %1%")
-       % forw_projector_sptr->parameter_info());
+       % forward_projector_for_mask_sptr->parameter_info());
 
   shared_ptr<ProjData> mask_projdata;
   if (run_in_2d_projdata)
     {
-      forw_projector_sptr->set_up(this->input_projdata_2d_sptr->get_proj_data_info_sptr(), this->mask_image_sptr);
+      forward_projector_for_mask_sptr->set_up(this->input_projdata_2d_sptr->get_proj_data_info_sptr(), this->mask_image_sptr);
 
       mask_projdata.reset(new ProjDataInMemory(this->input_projdata_2d_sptr->get_exam_info_sptr(),
                                                this->input_projdata_2d_sptr->get_proj_data_info_sptr()));
     }
   else
     {
-      forw_projector_sptr->set_up(this->input_projdata_sptr->get_proj_data_info_sptr(), this->mask_image_sptr);
+      forward_projector_for_mask_sptr->set_up(this->input_projdata_sptr->get_proj_data_info_sptr(), this->mask_image_sptr);
 
       mask_projdata.reset(new ProjDataInMemory(this->input_projdata_sptr->get_exam_info_sptr(),
                                                this->input_projdata_sptr->get_proj_data_info_sptr()));
     }
 
-  forw_projector_sptr->forward_project(*mask_projdata, *this->mask_image_sptr);
+  forward_projector_for_mask_sptr->forward_project(*mask_projdata, *this->mask_image_sptr);
 
   // add 1 to be able to use create_tail_mask_from_ACFs (which expects ACFs,
   // so complains if the threshold is too low)