diff --git a/webservice/webservice.py b/webservice/webservice.py
index f8932146aee3fa0ae6631b315dd0c250b9260ed8..ebdcac554983b1ab64662abd6c64bd45888375ea 100644
--- a/webservice/webservice.py
+++ b/webservice/webservice.py
@@ -176,7 +176,7 @@ async def change_config(socket, config, updated_config, karabo_id, instrument, c
                 if action != "data-mapping":
                     subconf[action][instrument] = instruments[instrument]
                 else:
-                    subconf[action][instrument] = instruments[karabo_id]
+                    subconf[action][karabo_id] = instruments[karabo_id]
             with open(fpath, "w") as wf:
                 wf.write(yaml.dump(subconf, default_flow_style=False))
     new_conf = None