diff --git a/pgp-encode.c b/pgp-encode.c
index 56332db2f3b73ff8fe541716d30a65fb10676f3d..2bbb90d6d5d2429d0c7175a5e5f4c3a915cec2fe 100644
--- a/pgp-encode.c
+++ b/pgp-encode.c
@@ -81,7 +81,7 @@ pgp_put_mpi(struct nettle_buffer *buffer, const mpz_t x)
   if (!p)
     return 0;
   
-  nettle_mpz_get_str_256(x, octets, p);
+  nettle_mpz_get_str_256(octets, p, x);
 
   return 1;
 }