diff --git a/Trigger/TrigSteer/TrigOutputHandling/python/TrigOutputHandlingConfig.py b/Trigger/TrigSteer/TrigOutputHandling/python/TrigOutputHandlingConfig.py
index 685efd720c95ea659aedd2a22e7bcae47f455bd1..b2215369d1d4c3655c790c7eaeb38b1875168bd6 100644
--- a/Trigger/TrigSteer/TrigOutputHandling/python/TrigOutputHandlingConfig.py
+++ b/Trigger/TrigSteer/TrigOutputHandling/python/TrigOutputHandlingConfig.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 
 from AthenaConfiguration.ComponentFactory import CompFactory
 
@@ -70,15 +70,6 @@ def TriggerEDMSerialiserToolCfg(name="Serialiser"):
    # Create and return a serialiser tool object
    serialiser = TriggerEDMSerialiserTool(name)
 
-   # Allow appending to the collections list
-   def merge_collection_list(a, b):
-      for item in b:
-         if item not in a:
-               a.append(item)
-      return a
-   serialiser._descriptors['CollectionsToSerialize'].semantics.merge = merge_collection_list
-
-
    from TrigEDMConfig.TriggerEDMRun3 import tpMap
    tpTool = CompFactory.TrigSerTPTool()
    tpTool.TPMap = tpMap()
diff --git a/Trigger/TrigSteer/TrigOutputHandling/src/TriggerEDMSerialiserTool.h b/Trigger/TrigSteer/TrigOutputHandling/src/TriggerEDMSerialiserTool.h
index 4a66e05b4ca63166fa4f362983d4a893edeebd48..e2e687125b986ab7180b7d3084ca8019fe2d2731 100644
--- a/Trigger/TrigSteer/TrigOutputHandling/src/TriggerEDMSerialiserTool.h
+++ b/Trigger/TrigSteer/TrigOutputHandling/src/TriggerEDMSerialiserTool.h
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
 */
 #ifndef TRIGOUTPUTHANDLING_TRIGGEREDMSERIALISERTOOL_H
 #define TRIGOUTPUTHANDLING_TRIGGEREDMSERIALISERTOOL_H
@@ -55,7 +55,8 @@ class TriggerEDMSerialiserTool: public extends<AthAlgTool, HLTResultMTMakerTool>
     "formatted like for AthenaOutputStream, e.g. TYPE#SG.aux1.aux2..etc. For xAOD classes the typedef type should be "
     "used and the _vN version number is automatically detected. For old T/P classes the persistent version has to be "
     "given. Module IDs following the semicolon are the HLT result ROB module IDs to which the collection should be "
-    "written. ID=0 is the main result, other IDs are used for data scouting."
+    "written. ID=0 is the main result, other IDs are used for data scouting.",
+    "OrderedSet<std::string>"
   };
   Gaudi::Property<bool> m_saveDynamic {
     this, "SaveDynamic", true, "If false skips serialising of dynamic variables. Use for test purpose only."