Index: src/natools-smaz_implementations-base_256.adb
==================================================================
--- src/natools-smaz_implementations-base_256.adb
+++ src/natools-smaz_implementations-base_256.adb
@@ -36,11 +36,11 @@
       else
          Code := 0;
 
          if not Variable_Length_Verbatim then
             Verbatim_Length
-              := Positive (Ada.Streams.Stream_Element'Last - Input_Byte) + 1;
+              := Natural (Ada.Streams.Stream_Element'Last - Input_Byte) + 1;
          elsif Input_Byte < Ada.Streams.Stream_Element'Last then
             Verbatim_Length
               := Positive (Ada.Streams.Stream_Element'Last - Input_Byte);
          else
             Offset := Offset + 1;