diff --git a/processing/post/vtk_addGridData.py b/processing/post/vtk_addGridData.py
index 34f01e7bf..5ed50b60e 100755
--- a/processing/post/vtk_addGridData.py
+++ b/processing/post/vtk_addGridData.py
@@ -67,7 +67,6 @@ elif vtk_ext == '.vtk':
   reader.Update()
   rGrid = reader.GetRectilinearGridOutput()
   writer = vtk.vtkXMLRectilinearGridWriter()
-  vtk_ext = '.vtr'
 elif vtk_ext == '.vtu':
   reader = vtk.vtkXMLUnstructuredGridReader()
   reader.SetFileName(options.vtk)
@@ -77,7 +76,7 @@ elif vtk_ext == '.vtu':
 else:
   parser.error('Unsupported VTK file type extension.')
 
-writer.SetFileName(vtk_file+vtk_ext)
+writer.SetFileName(vtk_file+'.'+writer.GetDefaultFileExtension())
 
 Npoints = rGrid.GetNumberOfPoints()
 Ncells  = rGrid.GetNumberOfCells()
diff --git a/processing/post/vtk_addPointCloudData.py b/processing/post/vtk_addPointCloudData.py
index 0a1cb1231..f37def80a 100755
--- a/processing/post/vtk_addPointCloudData.py
+++ b/processing/post/vtk_addPointCloudData.py
@@ -61,7 +61,6 @@ elif vtk_ext == '.vtk':
   reader.SetFileName(options.vtk)
   reader.Update()
   Polydata = reader.GetPolyDataOutput()
-  vtk_ext = '.vtp'
 else:
   parser.error('unsupported VTK file type extension.')
 
@@ -152,7 +151,7 @@ for name in filenames:
   writer = vtk.vtkXMLPolyDataWriter()
   writer.SetDataModeToBinary()
   writer.SetCompressorTypeToZLib()
-  writer.SetFileName(vtk_file+vtk_ext)
+  writer.SetFileName(vtk_file+'.'+writer.GetDefaultFileExtension())
   writer.SetInputData(Polydata)
   writer.Write()
 
diff --git a/processing/post/vtk_addRectilinearGridData.py b/processing/post/vtk_addRectilinearGridData.py
index 868fdc387..890b28fa8 100755
--- a/processing/post/vtk_addRectilinearGridData.py
+++ b/processing/post/vtk_addRectilinearGridData.py
@@ -64,7 +64,6 @@ elif vtk_ext == '.vtk':
   reader.SetFileName(options.vtk)
   reader.Update()
   rGrid = reader.GetRectilinearGridOutput()
-  vtk_ext = '.vtr'
 else:
   parser.error('unsupported VTK file type extension.')
 
@@ -161,7 +160,7 @@ for name in filenames:
   writer = vtk.vtkXMLRectilinearGridWriter()
   writer.SetDataModeToBinary()
   writer.SetCompressorTypeToZLib()
-  writer.SetFileName(vtk_file+vtk_ext)
+  writer.SetFileName(vtk_file+'.'+writer.GetDefaultFileExtension())
   writer.SetInputData(rGrid)
   writer.Write()