diff --git a/Code/Projections/otbPhysicalToRPCSensorModelImageFilter.h b/Code/Projections/otbPhysicalToRPCSensorModelImageFilter.h
index 9ad917599728073f61cf80ddab7b296be183329a..65f143f9bef839d9ce71799e74317b422a515f85 100644
--- a/Code/Projections/otbPhysicalToRPCSensorModelImageFilter.h
+++ b/Code/Projections/otbPhysicalToRPCSensorModelImageFilter.h
@@ -90,7 +90,7 @@ public:
   
   /** Set/Get the grid size*/
   itkSetMacro(GridSize, SizeType);
-  itkGetMacro(GridSize, SizeType);
+  itkGetConstReferenceMacro(GridSize, SizeType);
 
   /** Set/Get the DEM directory*/
   itkSetStringMacro(DEMDirectory);