diff --git a/src/surface_points_filter.cc b/src/surface_points_filter.cc
index 3b240e3..2de5261 100644
--- a/src/surface_points_filter.cc
+++ b/src/surface_points_filter.cc
@@ -59,12 +59,12 @@ vtkTypeBool SurfacePointsFilter::RequestData(
 			input->GetCellNeighbors(it->GetCellId(), facePoints,
 			                        neighborCells);
 			facePoints->Reset();
-			if (neighborCells->GetNumberOfIds() == 1) {
+			if (neighborCells->GetNumberOfIds() == 0) {
 				surfacePoints->InsertNextValue(idA);
-				isSurface->SetValue(idA, 1);
 				surfacePoints->InsertNextValue(idB);
-				isSurface->SetValue(idB, 1);
 				surfacePoints->InsertNextValue(idC);
+				isSurface->SetValue(idA, 1);
+				isSurface->SetValue(idB, 1);
 				isSurface->SetValue(idC, 1);
 			}
 		}