Index: src/natools-s_expressions-atom_buffers.ads
==================================================================
--- src/natools-s_expressions-atom_buffers.ads
+++ src/natools-s_expressions-atom_buffers.ads
@@ -25,11 +25,11 @@
 with Natools.S_Expressions.Atom_Refs;
 
 package Natools.S_Expressions.Atom_Buffers is
    pragma Preelaborate (Atom_Buffers);
 
-   type Atom_Buffer is tagged private;
+   type Atom_Buffer is tagged limited private;
    pragma Preelaborable_Initialization (Atom_Buffer);
 
    procedure Preallocate (Buffer : in out Atom_Buffer; Length : in Count);
       --  Preallocate enough memory to append Length octets without
       --  any further allocation.
@@ -69,11 +69,11 @@
    procedure Soft_Reset (Buffer : in out Atom_Buffer);
       --  Clear buffer keeping internal memory
 
 private
 
-   type Atom_Buffer is tagged record
+   type Atom_Buffer is tagged limited record
       Ref : Atom_Refs.Reference;
       Available, Used : Count := 0;
    end record;
 
 end Natools.S_Expressions.Atom_Buffers;