diff --git a/src/lib.rs b/src/lib.rs
index faaf7ac..b5cac49 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -23,7 +23,8 @@ pub use types::{
     Identifier, LetsEncrypt, NewAccount, NewOrder, OrderState, OrderStatus, Problem,
 };
 use types::{
-    DirectoryUrls, Empty, FinalizeRequest, Header, Jwk, KeyOrKeyId, Signer, SigningAlgorithm,
+    DirectoryUrls, Empty, FinalizeRequest, Header, JoseJson, Jwk, KeyOrKeyId, Signer,
+    SigningAlgorithm,
 };
 
 /// An ACME order as described in RFC 8555 (section 7.1.3)
@@ -361,7 +362,7 @@ impl Client {
         };
 
         let nonce = nonce.ok_or("no nonce found")?;
-        let body = signer.signed_json(payload, signer.header(&nonce, url))?;
+        let body = JoseJson::new(payload, signer.header(&nonce, url), signer)?;
         let request = Request::builder()
             .method(Method::POST)
             .uri(url)
diff --git a/src/types.rs b/src/types.rs
index c811588..6793190 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -261,14 +261,12 @@ pub(crate) struct JoseJson {
     pub(crate) signature: String,
 }
 
-pub(crate) trait Signer {
-    type Signature: AsRef<[u8]>;
-
-    fn signed_json(
-        &self,
+impl JoseJson {
+    pub(crate) fn new(
         payload: Option<&impl Serialize>,
         protected: Header<'_>,
-    ) -> Result<JoseJson, Error> {
+        signer: &impl Signer,
+    ) -> Result<Self, Error> {
         let protected = base64(&protected)?;
         let payload = match payload {
             Some(data) => base64(&data)?,
@@ -276,13 +274,17 @@ pub(crate) trait Signer {
         };
 
         let combined = format!("{protected}.{payload}");
-        let signature = self.sign(combined.as_bytes())?;
-        Ok(JoseJson {
+        let signature = signer.sign(combined.as_bytes())?;
+        Ok(Self {
             protected,
             payload,
             signature: BASE64_URL_SAFE_NO_PAD.encode(signature.as_ref()),
         })
     }
+}
+
+pub(crate) trait Signer {
+    type Signature: AsRef<[u8]>;
 
     fn header<'n, 'u: 'n, 's: 'u>(&'s self, nonce: &'n str, url: &'u str) -> Header<'n>;