diff --git a/src/crypto.ml b/src/crypto.ml
index aac1d07d..99cabfea 100644
--- a/src/crypto.ml
+++ b/src/crypto.ml
@@ -159,37 +159,35 @@ end = struct
      binary-encoded objects with just the R and S values *)
   type t = string
 
-  (* mirage_crypto: "The result is the concatenation of r and s, as specified in RFC 8032." *)
+  (* mirage_crypto:
+     "The result is the concatenation of r and s, as specified in RFC 8032." *)
   let sign ~key s = Mirage_crypto_ec.Ed25519.sign ~key s
 
   let verify ~key s ~msg =
     let b = Mirage_crypto_ec.Ed25519.verify ~key s ~msg in
     match b with
-    | false -> Error "signature verification failure: invalid signature"
+    | false -> Error "EddsaSignature verification: invalid signature"
     | true -> Ok ()
 
   let to_octets t = t
 
+  let check_size t =
+    match String.length t = 64 with
+    | false -> Error "EddsaSignature of_octets: data is not 64 bytes."
+    | true -> Ok ()
+
   let of_octets v =
-    match String.length v = 64 with
-    | false ->
-        Fmt.error "EddsaSignature.of_octets failure: data is not 64 bytes."
-    | true -> Ok v
+    let+ () = check_size v in
+    v
 
   let bin =
     let of_octets_exn t = of_octets t |> Result.get_ok in
     Bin.map (Bin.bytes 64) of_octets_exn to_octets
 
-  let check_size t =
-    match String.length t = 64 with
-    | false -> Error "EddsaSignature: invalid string length"
-    | true -> Ok ()
-
   let jsont =
     let of_b32 s =
       let* t = B32.decode s in
-      let+ () = check_size t in
-      t
+      of_octets t
     in
     let to_b32 = B32.encode in
     Jsont.of_of_string ~kind:"EddsaSignature" of_b32 ~enc:to_b32
diff --git a/src/signatures.ml b/src/signatures.ml
index 80cebad6..1d57405e 100644
--- a/src/signatures.ml
+++ b/src/signatures.ml
@@ -1,9 +1,7 @@
 (* TODO signatures
-   check with taler-wallet-core/src/crypto/cryptoImplementation.js
+   check with taler-wallet
    check signed/unsigned ints
-   check endianness
-
-   better handling of decoding failure *)
+   check endianness *)
 open Hash
 
 module Aliases = struct
@@ -177,8 +175,9 @@ end = struct
   type r = R.r
   type t = EddsaSignature.t
 
-  let sign_f ~f r = f (Bin.to_string R.bin r)
-  let verify_f ~f t r = f t ~msg:(Bin.to_string R.bin r)
+  let to_string = Bin.to_string R.bin
+  let sign_f ~f r = f (to_string r)
+  let verify_f ~f t r = f t ~msg:(to_string r)
   let jsont = EddsaSignature.jsont
   let caqti : EddsaSignature.t Caqti_type.t = EddsaSignature.caqti
   let to_octets t = EddsaSignature.to_octets t