diff --git a/swh/core/api/__init__.py b/swh/core/api/__init__.py
--- a/swh/core/api/__init__.py
+++ b/swh/core/api/__init__.py
@@ -152,7 +152,8 @@
 
             # Send the request.
             return self.post(meth._endpoint_path, post_data)
-        attributes[meth_name] = meth_
+        if meth_name not in attributes:
+            attributes[meth_name] = meth_
 
 
 class RPCClient(metaclass=MetaRPCClient):