diff --git a/src/cipher_block.ml b/src/cipher_block.ml
index 474b42df..6919fdff 100644
--- a/src/cipher_block.ml
+++ b/src/cipher_block.ml
@@ -243,12 +243,12 @@ module Modes = struct
     let derive cs =
       assert (String.length cs >= tagsize);
       let k = Bytes.create keysize in
-      Native.GHASH.keyinit cs 0 k;
+      Native.GHASH.keyinit cs k;
       Bytes.unsafe_to_string k
     let hash0 = Bytes.make tagsize '\x00'
     let digesti ~key i =
       let res = Bytes.copy hash0 in
-      i (fun cs -> Native.GHASH.ghash key res cs 0 (String.length cs));
+      i (fun cs -> Native.GHASH.ghash key res cs (String.length cs));
       Bytes.unsafe_to_string res
   end
 
diff --git a/src/native.ml b/src/native.ml
index fcc6592e..2dd72f46 100644
--- a/src/native.ml
+++ b/src/native.ml
@@ -30,8 +30,8 @@ end
 
 module GHASH = struct
   external keysize : unit -> int = "mc_ghash_key_size" [@@noalloc]
-  external keyinit : string -> int -> bytes -> unit = "mc_ghash_init_key" [@@noalloc]
-  external ghash : string -> bytes -> string -> int -> int -> unit = "mc_ghash" [@@noalloc]
+  external keyinit : string -> bytes -> unit = "mc_ghash_init_key" [@@noalloc]
+  external ghash : string -> bytes -> string -> int -> unit = "mc_ghash" [@@noalloc]
   external mode : unit -> int = "mc_ghash_mode" [@@noalloc]
 end
 
diff --git a/src/native/ghash_ctmul.c b/src/native/ghash_ctmul.c
index 8d517586..7788fd05 100644
--- a/src/native/ghash_ctmul.c
+++ b/src/native/ghash_ctmul.c
@@ -284,14 +284,14 @@ static inline void __copy (uint64_t key[2], uint32_t m[4]) {
   m[3] = key[1] >> 32;
 }
 
-CAMLprim value mc_ghash_init_key_generic (value key, value off, value m) {
+CAMLprim value mc_ghash_init_key_generic (value key, value m) {
   //push key at off into m
-  __copy ((uint64_t *) _st_uint8_off(key, off), (uint32_t *) m);
+  __copy ((uint64_t *) _st_uint8(key), (uint32_t *) m);
   return Val_unit;
 }
 
-CAMLprim value mc_ghash_generic (value m, value hash, value src, value off, value len) {
-  br_ghash_ctmul(Bp_val(hash), Bp_val(m), _st_uint8_off(src, off), Int_val(len));
+CAMLprim value mc_ghash_generic (value m, value hash, value src, value len) {
+  br_ghash_ctmul(Bp_val(hash), Bp_val(m), _st_uint8(src), Int_val(len));
   return Val_unit;
 }
 
diff --git a/src/native/ghash_generic.c b/src/native/ghash_generic.c
index 5bf5f2bf..2cc49532 100644
--- a/src/native/ghash_generic.c
+++ b/src/native/ghash_generic.c
@@ -95,15 +95,15 @@ CAMLprim value mc_ghash_key_size_generic (__unit ()) {
   return Val_int (sizeof (__uint128_t) * __t_size);
 }
 
-CAMLprim value mc_ghash_init_key_generic (value key, value off, value m) {
-  __derive ((uint64_t *) _st_uint8_off (key, off), (__uint128_t *) Bp_val (m));
+CAMLprim value mc_ghash_init_key_generic (value key, value m) {
+  __derive ((uint64_t *) _st_uint8 (key), (__uint128_t *) Bp_val (m));
   return Val_unit;
 }
 
 CAMLprim value
-mc_ghash_generic (value m, value hash, value src, value off, value len) {
+mc_ghash_generic (value m, value hash, value src, value len) {
   __ghash ((__uint128_t *) Bp_val (m), (uint64_t *) Bp_val (hash),
-           _st_uint8_off (src, off), Int_val (len) );
+           _st_uint8 (src), Int_val (len) );
   return Val_unit;
 }
 
diff --git a/src/native/ghash_pclmul.c b/src/native/ghash_pclmul.c
index 069c2b3b..58ca02ea 100644
--- a/src/native/ghash_pclmul.c
+++ b/src/native/ghash_pclmul.c
@@ -196,19 +196,19 @@ CAMLprim value mc_ghash_key_size (__unit ()) {
   return s;
 }
 
-CAMLprim value mc_ghash_init_key (value key, value off, value m) {
+CAMLprim value mc_ghash_init_key (value key, value m) {
   _mc_switch_accel(pclmul,
-    mc_ghash_init_key_generic(key, off, m),
-    __derive ((__m128i *) _st_uint8_off (key, off), (__m128i *) Bp_val (m)))
+    mc_ghash_init_key_generic(key, m),
+    __derive ((__m128i *) _st_uint8 (key), (__m128i *) Bp_val (m)))
   return Val_unit;
 }
 
 CAMLprim value
-mc_ghash (value k, value hash, value src, value off, value len) {
+mc_ghash (value k, value hash, value src, value len) {
   _mc_switch_accel(pclmul,
-    mc_ghash_generic(k, hash, src, off, len),
+    mc_ghash_generic(k, hash, src, len),
     __ghash ( (__m128i *) Bp_val (k), (__m128i *) Bp_val (hash),
-      (__m128i *) _st_uint8_off (src, off), Int_val (len) ))
+      (__m128i *) _st_uint8 (src), Int_val (len) ))
   return Val_unit;
 }
 
diff --git a/src/native/mirage_crypto.h b/src/native/mirage_crypto.h
index 11536e24..31b9d77a 100644
--- a/src/native/mirage_crypto.h
+++ b/src/native/mirage_crypto.h
@@ -102,10 +102,10 @@ mc_aes_dec_generic (value src, value off1, value dst, value off2, value rk, valu
 
 CAMLprim value mc_ghash_key_size_generic (__unit ());
 
-CAMLprim value mc_ghash_init_key_generic (value key, value off, value m);
+CAMLprim value mc_ghash_init_key_generic (value key, value m);
 
 CAMLprim value
-mc_ghash_generic (value m, value hash, value src, value off, value len);
+mc_ghash_generic (value m, value hash, value src, value len);
 
 CAMLprim value
 mc_xor_into_generic (value b1, value off1, value b2, value off2, value n);