diff --git a/compiler/tests-ocaml/lib-effects/marshal.ml b/compiler/tests-ocaml/lib-effects/marshal.ml
index 8788272372..6c754073e2 100644
--- a/compiler/tests-ocaml/lib-effects/marshal.ml
+++ b/compiler/tests-ocaml/lib-effects/marshal.ml
@@ -12,9 +12,10 @@ let _ =
       Some (fun k ->
           (* We have to make sure that neither the match nor the call
              to Marshal.to_string are eliminated, so we call
-             print_string and we return the result of the marshalling
+             print_string and we print the result of the marshalling
              function. *)
-          match print_string ""; Stdlib.Marshal.to_string k [] with
-          | x -> x
-          | exception ((*Invalid_argument*) _) -> print_endline "ok"; ""
+          match print_string "";
+            Stdlib.Marshal.to_string k [] with
+          | x -> Printf.printf "%S" x; assert false
+          | exception (Invalid_argument _) -> print_endline "ok"; ""
           ) }
diff --git a/compiler/tests-ocaml/lib-effects/marshal.reference b/compiler/tests-ocaml/lib-effects/marshal.reference
index a640b98b37..9766475a41 100644
--- a/compiler/tests-ocaml/lib-effects/marshal.reference
+++ b/compiler/tests-ocaml/lib-effects/marshal.reference
@@ -1 +1 @@
-Aok
+ok