Index: src/natools-s_expressions-atom_buffers.adb
==================================================================
--- src/natools-s_expressions-atom_buffers.adb
+++ src/natools-s_expressions-atom_buffers.adb
@@ -58,14 +58,17 @@
    end Preallocate;
 
 
    procedure Append (Buffer : in out Atom_Buffer; Data : in Atom) is
    begin
-      Preallocate (Buffer, Data'Length);
-      Buffer.Ref.Update.Data.all (Buffer.Used + 1 .. Buffer.Used + Data'Length)
-        := Data;
-      Buffer.Used := Buffer.Used + Data'Length;
+      if Data'Length > 0 then
+         Preallocate (Buffer, Data'Length);
+         Buffer.Ref.Update.Data.all
+           (Buffer.Used + 1 .. Buffer.Used + Data'Length)
+           := Data;
+         Buffer.Used := Buffer.Used + Data'Length;
+      end if;
    end Append;
 
 
    procedure Append (Buffer : in out Atom_Buffer; Data : in Octet) is
    begin