diff --git a/hosts/ocaml/bin/sx_server.ml b/hosts/ocaml/bin/sx_server.ml
index b2f703e3..f82a0df4 100644
--- a/hosts/ocaml/bin/sx_server.ml
+++ b/hosts/ocaml/bin/sx_server.ml
@@ -53,7 +53,14 @@ let rec serialize_value = function
   | Symbol s -> s
   | Keyword k -> ":" ^ k
   | List items | ListRef { contents = items } ->
-    "(list " ^ String.concat " " (List.map serialize_value items) ^ ")"
+    (* Lists with a symbol head are call expressions: (fn arg1 arg2).
+       Lists starting with data values are data: (list 1 2 3).
+       This distinction matters for the client parser. *)
+    (match items with
+     | (Symbol _ | Keyword _) :: _ ->
+       "(" ^ String.concat " " (List.map serialize_value items) ^ ")"
+     | _ ->
+       "(list " ^ String.concat " " (List.map serialize_value items) ^ ")")
   | Dict d ->
     let pairs = Hashtbl.fold (fun k v acc ->
       (Printf.sprintf ":%s %s" k (serialize_value v)) :: acc) d [] in