diff --git a/vendors/ocaml-hacl/readme.md b/vendors/ocaml-hacl/readme.md
index 120bafdf7..cb1cd5db0 100644
--- a/vendors/ocaml-hacl/readme.md
+++ b/vendors/ocaml-hacl/readme.md
@@ -1,2 +1,3 @@
 Tezos binding for Hacl*
 https://github.com/mitls/hacl-star/tree/master/snapshots/tezos
+commit b69319a0d3b71af8042f487d6a5bac8101edf2d0
diff --git a/vendors/ocaml-hacl/src/config/discover.ml b/vendors/ocaml-hacl/src/config/discover.ml
new file mode 100644
index 000000000..c6dbe1e9f
--- /dev/null
+++ b/vendors/ocaml-hacl/src/config/discover.ml
@@ -0,0 +1,11 @@
+let () =
+  (* inspired by https://github.com/vbmithr/ocaml-secp256k1-internal/blob/master/config/discover.ml *)
+  let ccopts = "-Ofast -march=native -mtune=native -m64 -fwrapv -fomit-frame-pointer -funroll-loops -Wall -Werror -Wfatal-errors" in
+  (* the important bit is -DKRML_NOUINT128 which enables the verified (but slow) implementation of UInt128 in FStar.c rather than the builtin __int128 which is only available on 64-bit platforms. *)
+  let ccopts32 = "-Ofast -fwrapv -fomit-frame-pointer -funroll-loops -DKRML_NOUINT128 -Wall -Werror -Wfatal-errors" in
+
+  let oc = open_out "c_flags.sexp" in
+  let sixtyfour = Sys.word_size = 64 in
+  let flags = if sixtyfour then ccopts else ccopts32 in
+  Printf.fprintf oc "(%s)%!" flags ;
+  close_out oc
diff --git a/vendors/ocaml-hacl/src/config/jbuild b/vendors/ocaml-hacl/src/config/jbuild
new file mode 100644
index 000000000..d96941edd
--- /dev/null
+++ b/vendors/ocaml-hacl/src/config/jbuild
@@ -0,0 +1,5 @@
+(jbuild_version 1)
+
+(executable
+ ((name discover)
+  (libraries (base stdio))))
diff --git a/vendors/ocaml-hacl/src/jbuild b/vendors/ocaml-hacl/src/jbuild
index 519cb83bf..7b7fb1042 100644
--- a/vendors/ocaml-hacl/src/jbuild
+++ b/vendors/ocaml-hacl/src/jbuild
@@ -22,5 +22,11 @@
                     Hacl_Salsa20
                     NaCl
                     Hacl_Unverified_Random))
-  (c_flags         (-O3 -Wall -Werror -Wfatal-errors))
+  (c_flags         (:include c_flags.sexp))
 ))
+
+; sets flags for 32/64 bits architectures
+(rule
+ ((targets (c_flags.sexp))
+  (deps    (config/discover.exe))
+  (action  (run ${<} -ocamlc ${OCAMLC}))))