diff --git a/src-ocaml/xor.ml b/src-ocaml/xor.ml
index 480f9d3..ca406ba 100644
--- a/src-ocaml/xor.ml
+++ b/src-ocaml/xor.ml
@@ -11,7 +11,9 @@ module type BUFFER = sig
   val sub : t -> int -> int -> t
   val copy : t -> t
   val benat_to_cpu : t -> int -> nativeint
+  val byte_to_cpu : t -> int -> int
   val cpu_to_benat : t -> int -> nativeint -> unit
+  val cpu_to_byte : t -> int -> int -> unit
 end
 
 let imin (a : int) (b : int) = if a < b then a else b
@@ -33,10 +35,8 @@ module Make (B : BUFFER) = struct
       i := !i + size_of_long
     done ;
     while !n > 0 do
-      B.cpu_to_benat dst (dst_off + !i)
-        Nat.(
-          B.benat_to_cpu src (src_off + !i)
-          lxor B.benat_to_cpu dst (dst_off + !i)) ;
+      B.cpu_to_byte dst (dst_off + !i)
+        (B.byte_to_cpu src (src_off + !i) lxor B.byte_to_cpu dst (dst_off + !i)) ;
       incr i ;
       decr n
     done
diff --git a/src/digestif_bi.ml b/src/digestif_bi.ml
index 57cd475..97cd8af 100644
--- a/src/digestif_bi.ml
+++ b/src/digestif_bi.ml
@@ -48,6 +48,8 @@ let blit_from_bytes src src_off dst dst_off len =
 external swap32 : int32 -> int32 = "%bswap_int32"
 external swap64 : int64 -> int64 = "%bswap_int64"
 external swapnat : nativeint -> nativeint = "%bswap_native"
+external byte_to_cpu : t -> int -> int = "%caml_ba_unsafe_ref_1"
+external cpu_to_byte : t -> int -> int -> unit = "%caml_ba_unsafe_set_1"
 
 let cpu_to_be32 s i v =
   if Sys.big_endian then unsafe_set_32 s i v else unsafe_set_32 s i (swap32 v)
diff --git a/src/digestif_by.ml b/src/digestif_by.ml
index 26eb450..a55bae4 100644
--- a/src/digestif_by.ml
+++ b/src/digestif_by.ml
@@ -33,6 +33,8 @@ let rpad a size x =
 external swap32 : int32 -> int32 = "%bswap_int32"
 external swap64 : int64 -> int64 = "%bswap_int64"
 external swapnat : nativeint -> nativeint = "%bswap_native"
+external cpu_to_byte : t -> int -> int -> unit = "%bytes_unsafe_set"
+external byte_to_cpu : t -> int -> int = "%bytes_unsafe_get"
 
 let cpu_to_be32 s i v =
   if Sys.big_endian then unsafe_set_32 s i v else unsafe_set_32 s i (swap32 v)