diff --git a/hosts/ocaml/lib/sx_ref.ml b/hosts/ocaml/lib/sx_ref.ml
index 9c9a2f22..f42dc9c7 100644
--- a/hosts/ocaml/lib/sx_ref.ml
+++ b/hosts/ocaml/lib/sx_ref.ml
@@ -382,15 +382,16 @@ and expand_macro mac raw_args env =
 and cek_run state =
   let s = ref state in
   (try
+    let n = ref 0 in
     while not (match cek_terminal_p !s with Bool true -> true | _ -> false) do
       s := cek_step !s;
-      let n = Atomic.fetch_and_add _step_count 1 in
-      if n land 4095 = 0 then begin
+      incr n;
+      if !n land 4095 = 0 then begin
         let lim = Atomic.get _step_limit in
-        if lim > 0 && n >= lim then
-          raise (Eval_error (Printf.sprintf "Render step limit exceeded (%d steps)" n));
-        if n land 1048575 = 0 && n > 0 then
-          Printf.eprintf "[cek] %d steps, phase=%s control=%s\n%!" n
+        if lim > 0 && !n >= lim then
+          raise (Eval_error (Printf.sprintf "Render step limit exceeded (%d steps)" !n));
+        if !n land 1048575 = 0 then
+          Printf.eprintf "[cek] %d steps, phase=%s control=%s\n%!" !n
             (match cek_phase !s with String p -> p | _ -> "?")
             (String.sub (Sx_runtime.value_to_str (cek_control !s)) 0
               (min 80 (String.length (Sx_runtime.value_to_str (cek_control !s)))))