diff --git a/test/fiber/t_fib1.ml b/test/fiber/t_fib1.ml
index 84c4a667..09c033f6 100644
--- a/test/fiber/t_fib1.ml
+++ b/test/fiber/t_fib1.ml
@@ -49,22 +49,21 @@ let logf = Log_.logf
 
 let () =
   Printf.printf "============\nstart\n";
+  let@ nursery = F.Nursery.with_create_top ~on:runner () in
   let clock = ref TS.init in
   let fib =
-    F.spawn_top ~on:runner @@ fun () ->
+    F.spawn nursery @@ fun nursery ->
     let subs =
       List.init 5 (fun i ->
-          F.spawn_link ~protect:false @@ fun () ->
+          F.spawn nursery ~protect:false @@ fun _n ->
           Thread.delay (float i *. 0.01);
           i)
     in
 
-    ignore
-      (F.spawn_link ~protect:false @@ fun () ->
-       Thread.delay 0.4;
-       TS.tick clock;
-       logf !clock "other fib done"
-        : _ F.t);
+    F.spawn_ignore nursery ~protect:false (fun _n ->
+        Thread.delay 0.4;
+        TS.tick clock;
+        logf !clock "other fib done");
 
     logf (TS.tick_get clock) "wait for subs";
     List.iteri
@@ -92,8 +91,9 @@ let () =
   Printf.printf "============\nstart\n";
 
   let clock = ref TS.init in
+  let@ nursery = F.Nursery.with_create_top ~on:runner () in
   let fib =
-    F.spawn_top ~on:runner @@ fun () ->
+    F.spawn nursery @@ fun nursery ->
     let@ () =
       F.with_self_cancel_callback (fun ebt ->
           logf (TS.tick_get clock) "main fiber cancelled with %s"
@@ -104,7 +104,7 @@ let () =
     let subs =
       List.init 10 (fun i ->
           let clock = ref (0 :: i :: !clock) in
-          F.spawn_link ~protect:false @@ fun () ->
+          F.spawn nursery ~protect:false @@ fun _n ->
           let@ () =
             F.with_self_cancel_callback (fun _ ->
                 logf (TS.tick_get clock) "sub-fiber %d was cancelled" i)
@@ -126,11 +126,9 @@ let () =
           | Error _ -> logf (i :: post) "fiber %d resolved as error" i))
       subs;
 
-    ignore
-      (F.spawn_link ~protect:false @@ fun () ->
-       Thread.delay 0.2;
-       logf (TS.tick_get clock) "other fib done"
-        : _ F.t);
+    F.spawn_ignore nursery ~protect:false (fun _n ->
+        Thread.delay 0.2;
+        logf (TS.tick_get clock) "other fib done");
 
     logf (TS.tick_get clock) "wait for subs";
     List.iteri
diff --git a/test/fiber/t_fls.ml b/test/fiber/t_fls.ml
index 3c3ae8fd..47fd21c4 100644
--- a/test/fiber/t_fls.ml
+++ b/test/fiber/t_fls.ml
@@ -96,6 +96,7 @@ module Render = struct
 end
 
 let run ~pool ~pool_name () =
+  let@ nursery = F.Nursery.with_create_top ~on:pool () in
   let tracer = Tracer.create () in
 
   let sub_sub_child ~idx ~idx_child ~idx_sub ~idx_sub_sub () =
@@ -110,7 +111,7 @@ let run ~pool ~pool_name () =
     done
   in
 
-  let sub_child ~idx ~idx_child ~idx_sub () =
+  let sub_child ~idx ~idx_child ~idx_sub nursery =
     let@ () =
       Tracer.with_span tracer (spf "child_%d.%d.%d" idx idx_child idx_sub)
     in
@@ -122,19 +123,19 @@ let run ~pool ~pool_name () =
 
     let subs =
       List.init 2 (fun idx_sub_sub ->
-          F.spawn_link ~protect:true (fun () ->
+          F.spawn ~protect:true nursery (fun _nursery ->
               sub_sub_child ~idx ~idx_child ~idx_sub ~idx_sub_sub ()))
     in
     List.iter F.await subs
   in
 
-  let top_child ~idx ~idx_child () =
+  let top_child ~idx ~idx_child nursery =
     let@ () = Tracer.with_span tracer (spf "child.%d.%d" idx idx_child) in
 
     let subs =
       List.init 2 (fun k ->
-          F.spawn_link ~protect:true @@ fun () ->
-          sub_child ~idx ~idx_child ~idx_sub:k ())
+          F.spawn nursery ~protect:true @@ fun nursery ->
+          sub_child ~idx ~idx_child ~idx_sub:k nursery)
     in
 
     let@ () =
@@ -144,12 +145,13 @@ let run ~pool ~pool_name () =
     List.iter F.await subs
   in
 
-  let top idx =
+  let top nursery idx =
     let@ () = Tracer.with_span tracer (spf "top_%d" idx) in
 
     let subs =
       List.init 5 (fun j ->
-          F.spawn_link ~protect:true @@ fun () -> top_child ~idx ~idx_child:j ())
+          F.spawn nursery ~protect:true @@ fun nursery ->
+          top_child ~idx ~idx_child:j nursery)
     in
 
     List.iter F.await subs
@@ -157,7 +159,7 @@ let run ~pool ~pool_name () =
 
   Printf.printf "run test on pool = %s\n" pool_name;
   let fibs =
-    List.init 8 (fun idx -> F.spawn_top ~on:pool (fun () -> top idx))
+    List.init 8 (fun idx -> F.spawn nursery (fun nursery -> top nursery idx))
   in
   List.iter F.wait_block_exn fibs;