Index: src/natools-string_slices-slice_sets.adb
==================================================================
--- src/natools-string_slices-slice_sets.adb
+++ src/natools-string_slices-slice_sets.adb
@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
--- Copyright (c) 2013, Natacha Porté                                        --
+-- Copyright (c) 2013-2016, Natacha Porté                                   --
 --                                                                          --
 -- Permission to use, copy, modify, and distribute this software for any    --
 -- purpose with or without fee is hereby granted, provided that the above   --
 -- copyright notice and this permission notice appear in all copies.        --
 --                                                                          --
@@ -565,11 +565,11 @@
       Set.Bounds.Insert (Bounds);
    end Add_Slice;
 
 
    procedure Add_Slice (Set : in out Slice_Set; S : in Slice) is
-      use type String_Refs.Reference;
+      use type String_Refs.Immutable_Reference;
    begin
       if S.Bounds.Length = 0 then
          return;
       end if;
 
@@ -621,11 +621,11 @@
       Include_Range (Set.Bounds, Bounds);
    end Include_Slice;
 
 
    procedure Include_Slice (Set : in out Slice_Set; S : in Slice) is
-      use type String_Refs.Reference;
+      use type String_Refs.Immutable_Reference;
    begin
       if S.Bounds.Length = 0 then
          return;
       end if;
 

Index: src/natools-string_slices-slice_sets.ads
==================================================================
--- src/natools-string_slices-slice_sets.ads
+++ src/natools-string_slices-slice_sets.ads
@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
--- Copyright (c) 2013, Natacha Porté                                        --
+-- Copyright (c) 2013-2016, Natacha Porté                                   --
 --                                                                          --
 -- Permission to use, copy, modify, and distribute this software for any    --
 -- purpose with or without fee is hereby granted, provided that the above   --
 -- copyright notice and this permission notice appear in all copies.        --
 --                                                                          --
@@ -225,9 +225,9 @@
       --  Perform ensemble union and subtraction of index sets
 
 
    type Slice_Set is tagged record
       Bounds : Range_Set;
-      Ref : String_Refs.Reference;
+      Ref : String_Refs.Immutable_Reference;
    end record;
 
 end Natools.String_Slices.Slice_Sets;