diff --git a/extras/lex/lex.m b/extras/lex/lex.m
index c6c7930..fd8ed94 100644
--- a/extras/lex/lex.m
+++ b/extras/lex/lex.m
@@ -730,7 +730,7 @@ anybut(S0) = R :-
                     char.to_int(C, X),
                     not string.contains_char(S0, C)
                 ),
-                0x01 `..` 0xff
+                0x01 `..` 0x7f
             )
         ),
     R = any(S).