diff --git a/Makefile b/Makefile
index 7b4e63d1..8ca1e86a 100644
--- a/Makefile
+++ b/Makefile
@@ -9,6 +9,9 @@ clean:
 test:
 	@dune runtest $(DUNE_OPTS)
 
+test-autopromote:
+	@dune runtest $(DUNE_OPTS) --auto-promote
+
 doc:
 	@dune build $(DUNE_OPTS) @doc
 
diff --git a/test/fiber/t_fls.ml b/test/fiber/t_fls.ml
index be6deab1..ca397ed0 100644
--- a/test/fiber/t_fls.ml
+++ b/test/fiber/t_fls.ml
@@ -7,7 +7,7 @@ module FLS = Moonpool_fib.Fls
 
 type span_id = int
 
-let k_parent : span_id option FLS.t = FLS.create ()
+let k_parent : span_id Hmap.key = Hmap.Key.create ()
 let ( let@ ) = ( @@ )
 let spf = Printf.sprintf
 
@@ -39,10 +39,10 @@ module Tracer = struct
 
   let with_span self name f =
     let id = Span.new_id_ () in
-    let parent = FLS.get ~default:None k_parent in
+    let parent = FLS.get_in_local_hmap_opt k_parent in
     let span = { Span.id; parent; msg = name } in
     add self span;
-    FLS.with_value k_parent (Some id) f
+    FLS.with_in_local_hmap k_parent id f
 end
 
 module Render = struct