Index: src/natools-s_expressions-encodings.adb
==================================================================
--- src/natools-s_expressions-encodings.adb
+++ src/natools-s_expressions-encodings.adb
@@ -77,11 +77,11 @@
                      Has_High := True;
                   end if;
                end if;
             end loop;
             if Has_High then
-               Result (O) := Decode_Hex (High, 0);
+               Result (O) := Decode_Hex (High, Digit_0);
                O := O + 1;
             end if;
             pragma Assert (O - 1 = Result'Last);
          end;
       end return;