Index: src/natools-s_expressions-parsers.ads
==================================================================
--- src/natools-s_expressions-parsers.ads
+++ src/natools-s_expressions-parsers.ads
@@ -120,12 +120,12 @@
       Lock_Stack : Lockable.Lock_Stack;
       Locked : Boolean := False;
    end record;
 
    type Stream_Parser (Input : access Ada.Streams.Root_Stream_Type'Class) is
-     new Parser with null record;
+     limited new Parser with null record;
 
    overriding procedure Read_More
      (Self : in out Stream_Parser;
       Buffer : out Atom_Buffers.Atom_Buffer);
 
 end Natools.S_Expressions.Parsers;

Index: src/natools-s_expressions-printers-pretty.ads
==================================================================
--- src/natools-s_expressions-printers-pretty.ads
+++ src/natools-s_expressions-printers-pretty.ads
@@ -134,12 +134,12 @@
       Indent_Level : Screen_Offset := 0;
       Need_Blank   : Boolean := False;
    end record;
 
    type Stream_Printer (Stream : access Ada.Streams.Root_Stream_Type'Class) is
-     new Printer with null record;
+     limited new Printer with null record;
 
    overriding procedure Write_Raw
      (Output : in out Stream_Printer;
       Data : in Ada.Streams.Stream_Element_Array);
 
 end Natools.S_Expressions.Printers.Pretty;