diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7cc4c7f..483e437 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ### Added
 ### Changed
+- The `ClientAgentSigner` function `add_credentials` no longer takes `self` as mutable. This wasn't required by the 
+  function implementation.
+
 ### Fixed
 ### Removed
 
diff --git a/src/signing/client_signing.rs b/src/signing/client_signing.rs
index 1009278..b1ac23d 100644
--- a/src/signing/client_signing.rs
+++ b/src/signing/client_signing.rs
@@ -35,7 +35,7 @@ impl ClientAgentSigner {
         }
     }
 
-    pub fn add_credentials(&mut self, cell_id: CellId, credentials: SigningCredentials) {
+    pub fn add_credentials(&self, cell_id: CellId, credentials: SigningCredentials) {
         self.credentials.write().insert(cell_id, credentials);
     }
 }