diff --git a/Filters/Core/CMakeLists.txt b/Filters/Core/CMakeLists.txt
index b015c6571d50f4e96f4dedb1bc8e7f8109bd24af..78b39cdbb35b68ba4be01432f2d0b9da09050428 100644
--- a/Filters/Core/CMakeLists.txt
+++ b/Filters/Core/CMakeLists.txt
@@ -125,9 +125,10 @@ set(classes
   vtkVoronoi2D
   vtkWindowedSincPolyDataFilter)
 
-set(headers
-    vtk3DLinearGridInternal.h)
+set(private_headers
+  vtk3DLinearGridInternal.h)
 
 vtk_module_add_module(VTK::FiltersCore
-  CLASSES ${classes})
+  CLASSES ${classes}
+  PRIVATE_HEADERS ${private_headers})
 vtk_add_test_mangling(VTK::FiltersCore)