diff --git a/_tags b/_tags
index 825dc26..2e4613b 100644
--- a/_tags
+++ b/_tags
@@ -27,7 +27,7 @@
 <bench/*.ml{,i}>: pkg_benchmark
 <bench/*.ml{,i}>: use_sequence
 # OASIS_STOP
-true: bin_annot, color(always)
+true: safe_string, bin_annot, color(always)
 <**/*.ml>: warn(+a-4-44-48@8)
 <src/bigarray/*.ml>: warn(-33)
 true: mark_tag_used
diff --git a/src/Sequence.ml b/src/Sequence.ml
index 47b8f70..aa0e350 100644
--- a/src/Sequence.ml
+++ b/src/Sequence.ml
@@ -1107,7 +1107,7 @@ let to_buffer seq buf =
 (*$R
   let b = Buffer.create 4 in
   "hello world"
-    |> of_str |> rev |> map Char.uppercase
+    |> of_str |> rev |> map Char.uppercase_ascii
     |> (fun seq -> to_buffer seq b);
   OUnit.assert_equal "DLROW OLLEH" (Buffer.contents b);
 *)