diff --git a/shared/comm-opaque2/src/server/register.rs b/shared/comm-opaque2/src/server/register.rs
index e84696045..865332b88 100644
--- a/shared/comm-opaque2/src/server/register.rs
+++ b/shared/comm-opaque2/src/server/register.rs
@@ -1,40 +1,40 @@
 use opaque_ke::{errors::ProtocolError, ServerRegistration};
 use opaque_ke::{RegistrationRequest, RegistrationUpload, ServerSetup};
 
 use crate::Cipher;
 
 pub struct Registration {}
 
 impl Registration {
   pub fn new() -> Registration {
     Registration {}
   }
 
   pub fn start(
     &self,
     server_setup: &ServerSetup<Cipher>,
     payload: &[u8],
     credential_identifier: &[u8],
   ) -> Result<Vec<u8>, ProtocolError> {
     let upload = RegistrationRequest::deserialize(payload)?;
     let result = ServerRegistration::<Cipher>::start(
       server_setup,
       upload,
       credential_identifier,
     )?;
     Ok(result.message.serialize().to_vec())
   }
 
   pub fn finish(
-    &mut self,
+    &self,
     response_payload: &[u8],
   ) -> Result<Vec<u8>, ProtocolError> {
     let upload_payload =
       RegistrationUpload::<Cipher>::deserialize(response_payload)?;
     Ok(
       ServerRegistration::finish(upload_payload)
         .serialize()
         .to_vec(),
     )
   }
 }