diff --git a/src/secmod.mli b/src/secmod.mli
index ba897b50..3c022ce1 100644
--- a/src/secmod.mli
+++ b/src/secmod.mli
@@ -2,6 +2,7 @@ open Crypto
 
 type t
 
+val sign : ('r -> string) -> (eddsa_sig -> 't) -> 'r -> 't
 val get_sm_key_priv : t -> eddsa_priv
 val get_sm_key_pub : t -> eddsa_pub
 val get_signkeys : t -> Signkey_data.t list