diff --git a/qtest/Makefile b/qtest/Makefile
index 294dd4c..82e964e 100644
--- a/qtest/Makefile
+++ b/qtest/Makefile
@@ -1,6 +1,6 @@
 
 QTEST_PREAMBLE='open Iter_shims_;; '
-DONTTEST=../src/iterLabels.ml ../src/mkflags.ml ../src/mkshims.ml ../src/bigarray/mkshims.ml
+DONTTEST=../src/iterLabels.ml ../src/mkshims.ml ../src/bigarray/mkshims.ml
 QTESTABLE=$(filter-out $(DONTTEST), \
 	$(wildcard ../src/*.ml) \
 	$(wildcard ../src/*.mli) \
diff --git a/src/Iter.mli b/src/Iter.mli
index 973d620..71557dd 100644
--- a/src/Iter.mli
+++ b/src/Iter.mli
@@ -849,3 +849,4 @@ module IO : sig
     string -> Bytes.t t -> unit
   (** @since 0.5.4 *)
 end
+
diff --git a/src/bench/bench_persistent.ml b/src/bench/bench_persistent.ml
index e132426..b063646 100644
--- a/src/bench/bench_persistent.ml
+++ b/src/bench/bench_persistent.ml
@@ -1,3 +1,5 @@
+[@@@ocaml.warning "-5"]
+
 module MList = struct
   type 'a t = {
     content : 'a array;   (* elements of the node *)
diff --git a/src/bench/benchs.ml b/src/bench/benchs.ml
index 3e9149a..d2a17e2 100644
--- a/src/bench/benchs.ml
+++ b/src/bench/benchs.ml
@@ -2,6 +2,8 @@
 module S = Iter
 open Iter.Infix
 
+[@@@ocaml.warning "-5"]
+
 let small = [10;20;50;100;500]
 let medium = small @ [1000;10_000;100_000]
 let big = medium @ [500_000; 1_000_000; 2_000_000]
diff --git a/src/mkflags.ml b/src/mkflags.ml
deleted file mode 100644
index e6edba0..0000000
--- a/src/mkflags.ml
+++ /dev/null
@@ -1,14 +0,0 @@
-
- let () =
-   let major, minor =
-     Scanf.sscanf Sys.ocaml_version "%u.%u"
-       (fun major minor -> major, minor)
-   in
-   let after_4_3 = (major, minor) >= (4, 3) in
-   let flags_file = open_out "flambda.flags" in
-   if after_4_3 then (
-     output_string flags_file "(-O3 -unbox-closures -unbox-closures-factor 20 -color always)\n";
-   ) else (
-     output_string flags_file "()\n";
-   );
-   close_out flags_file