diff --git a/nym-registration-client/src/builder/config.rs b/nym-registration-client/src/builder/config.rs
index 2362c51817..4132365042 100644
--- a/nym-registration-client/src/builder/config.rs
+++ b/nym-registration-client/src/builder/config.rs
@@ -343,6 +343,7 @@ impl BuilderConfigBuilder {
     }
 
     #[cfg(unix)]
+    #[must_use]
     pub fn connection_fd_callback(
         mut self,
         connection_fd_callback: Arc<dyn Fn(RawFd) + Send + Sync>,