diff --git a/src/surface_points_filter.cc b/src/surface_points_filter.cc
index 7d1358b..6b73428 100644
--- a/src/surface_points_filter.cc
+++ b/src/surface_points_filter.cc
@@ -10,6 +10,8 @@
 #include <vtkStaticCellLinks.h>
 #include <vtkIntArray.h>
 
+#include <set>
+
 
 
 vtkStandardNewMacro(SurfacePointsFilter);
@@ -46,6 +48,7 @@ vtkTypeBool SurfacePointsFilter::RequestData(
 
 	vtkNew<vtkIdList> neighborCells;
 	vtkNew<vtkIdList> facePoints;
+	std::set<vtkIdType> surfacePointsSet;
 	auto *it = input->NewCellIterator();
 	for (it->InitTraversal(); !it->IsDoneWithTraversal(); it->GoToNextCell()) {
 		vtkIdList *cellPointIds = it->GetPointIds();
@@ -60,15 +63,19 @@ vtkTypeBool SurfacePointsFilter::RequestData(
 			                        neighborCells);
 			facePoints->Reset();
 			if (neighborCells->GetNumberOfIds() == 0) {
-				surfacePoints->InsertNextValue(idA);
-				surfacePoints->InsertNextValue(idB);
-				surfacePoints->InsertNextValue(idC);
+				surfacePointsSet.insert(idA);
+				surfacePointsSet.insert(idB);
+				surfacePointsSet.insert(idC);
 				isSurface->SetValue(idA, 1);
 				isSurface->SetValue(idB, 1);
 				isSurface->SetValue(idC, 1);
 			}
 		}
 	}
+	surfacePoints->Allocate(surfacePointsSet.size());
+	for (const vtkIdType &id : surfacePointsSet) {
+		surfacePoints->InsertNextValue(id);
+	}
 
 	output->GetPointData()->SetScalars(isSurface);
 	output->GetFieldData()->AddArray(surfacePoints);