diff --git a/Framework/AnalysisSupport/src/AODWriterHelpers.cxx b/Framework/AnalysisSupport/src/AODWriterHelpers.cxx
index 2b1b4f880d1ee..40d2189ea96d0 100644
--- a/Framework/AnalysisSupport/src/AODWriterHelpers.cxx
+++ b/Framework/AnalysisSupport/src/AODWriterHelpers.cxx
@@ -269,145 +269,149 @@ AlgorithmSpec AODWriterHelpers::getOutputObjHistWriter(ConfigContext const& ctx)
 
     callbacks.set<CallbackService::Id::EndOfStream>(endofdatacb);
     return [inputObjects, objmap, tskmap](ProcessingContext& pc) mutable -> void {
-      auto const& ref = pc.inputs().get("x");
-      if (!ref.header) {
-        LOG(error) << "Header not found";
-        return;
-      }
-      auto datah = o2::header::get<o2::header::DataHeader*>(ref.header);
-      if (!datah) {
-        LOG(error) << "No data header in stack";
-        return;
-      }
+      auto mergePart = [&inputObjects, &objmap, &tskmap](DataRef const& ref) {
+        if (!ref.header) {
+          LOG(error) << "Header not found";
+          return;
+        }
+        auto datah = o2::header::get<o2::header::DataHeader*>(ref.header);
+        if (!datah) {
+          LOG(error) << "No data header in stack";
+          return;
+        }
 
-      if (!ref.payload) {
-        LOGP(error, "Payload not found for {}/{}/{}", datah->dataOrigin.as<std::string>(), datah->dataDescription.as<std::string>(), datah->subSpecification);
-        return;
-      }
+        if (!ref.payload) {
+          LOGP(error, "Payload not found for {}/{}/{}", datah->dataOrigin.as<std::string>(), datah->dataDescription.as<std::string>(), datah->subSpecification);
+          return;
+        }
 
-      auto objh = o2::header::get<o2::framework::OutputObjHeader*>(ref.header);
-      if (!objh) {
-        LOGP(error, "No output object header in stack of {}/{}/{}", datah->dataOrigin.as<std::string>(), datah->dataDescription.as<std::string>(), datah->subSpecification);
-        return;
-      }
+        auto objh = o2::header::get<o2::framework::OutputObjHeader*>(ref.header);
+        if (!objh) {
+          LOGP(error, "No output object header in stack of {}/{}/{}", datah->dataOrigin.as<std::string>(), datah->dataDescription.as<std::string>(), datah->subSpecification);
+          return;
+        }
 
-      InputObject obj;
-      FairInputTBuffer tm(const_cast<char*>(ref.payload), static_cast<int>(datah->payloadSize));
-      tm.InitMap();
-      obj.kind = tm.ReadClass();
-      tm.SetBufferOffset(0);
-      tm.ResetMap();
-      if (obj.kind == nullptr) {
-        LOGP(error, "Cannot read class info from buffer of {}/{}/{}", datah->dataOrigin.as<std::string>(), datah->dataDescription.as<std::string>(), datah->subSpecification);
-        return;
-      }
+        InputObject obj;
+        FairInputTBuffer tm(const_cast<char*>(ref.payload), static_cast<int>(datah->payloadSize));
+        tm.InitMap();
+        obj.kind = tm.ReadClass();
+        tm.SetBufferOffset(0);
+        tm.ResetMap();
+        if (obj.kind == nullptr) {
+          LOGP(error, "Cannot read class info from buffer of {}/{}/{}", datah->dataOrigin.as<std::string>(), datah->dataDescription.as<std::string>(), datah->subSpecification);
+          return;
+        }
 
-      auto policy = objh->mPolicy;
-      auto sourceType = objh->mSourceType;
-      auto hash = objh->mTaskHash;
+        auto policy = objh->mPolicy;
+        auto sourceType = objh->mSourceType;
+        auto hash = objh->mTaskHash;
 
-      obj.obj = tm.ReadObjectAny(obj.kind);
-      auto* named = static_cast<TNamed*>(obj.obj);
-      obj.name = named->GetName();
-      auto hpos = std::find_if(tskmap.begin(), tskmap.end(), [&](auto&& x) { return x.id == hash; });
-      if (hpos == tskmap.end()) {
-        LOG(error) << "No task found for hash " << hash;
-        return;
-      }
-      auto taskname = hpos->name;
-      auto opos = std::find_if(objmap.begin(), objmap.end(), [&](auto&& x) { return x.id == hash; });
-      if (opos == objmap.end()) {
-        LOG(error) << "No object list found for task " << taskname << " (hash=" << hash << ")";
-        return;
-      }
-      auto objects = opos->bindings;
-      if (std::find(objects.begin(), objects.end(), obj.name) == objects.end()) {
-        LOG(error) << "No object " << obj.name << " in map for task " << taskname;
-        return;
-      }
-      auto nameHash = runtime_hash(obj.name.c_str());
-      InputObjectRoute key{obj.name, nameHash, taskname, hash, policy, sourceType};
-      auto existing = std::find_if(inputObjects->begin(), inputObjects->end(), [&](auto&& x) { return (x.first.uniqueId == nameHash) && (x.first.taskHash == hash); });
-      // If it's the first one, we just add it to the list.
-      if (existing == inputObjects->end()) {
-        obj.count = objh->mPipelineSize;
-        inputObjects->push_back(std::make_pair(key, obj));
-        existing = inputObjects->end() - 1;
-      } else {
-        obj.count = existing->second.count;
-        // Otherwise, we merge it with the existing one.
-        auto merger = existing->second.kind->GetMerge();
-        if (!merger) {
-          LOG(error) << "Already one unmergeable object found for " << obj.name;
+        obj.obj = tm.ReadObjectAny(obj.kind);
+        auto* named = static_cast<TNamed*>(obj.obj);
+        obj.name = named->GetName();
+        auto hpos = std::find_if(tskmap.begin(), tskmap.end(), [&](auto&& x) { return x.id == hash; });
+        if (hpos == tskmap.end()) {
+          LOG(error) << "No task found for hash " << hash;
           return;
         }
-        TList coll;
-        coll.Add(static_cast<TObject*>(obj.obj));
-        merger(existing->second.obj, &coll, nullptr);
-      }
-      // We expect as many objects as the pipeline size, for
-      // a given object name and task hash.
-      existing->second.count -= 1;
-
-      if (existing->second.count != 0) {
-        return;
-      }
-      // Write the object here.
-      auto route = existing->first;
-      auto entry = existing->second;
-      auto file = ROOTfileNames.find(route.policy);
-      if (file == ROOTfileNames.end()) {
-        return;
-      }
-      auto filename = file->second;
-      if (f[route.policy] == nullptr) {
-        f[route.policy] = TFile::Open(filename.c_str(), "RECREATE");
-      }
-      auto nextDirectory = route.directory;
-      if ((nextDirectory != currentDirectory) || (filename != currentFile)) {
-        if (!f[route.policy]->FindKey(nextDirectory.c_str())) {
-          f[route.policy]->mkdir(nextDirectory.c_str());
+        auto taskname = hpos->name;
+        auto opos = std::find_if(objmap.begin(), objmap.end(), [&](auto&& x) { return x.id == hash; });
+        if (opos == objmap.end()) {
+          LOG(error) << "No object list found for task " << taskname << " (hash=" << hash << ")";
+          return;
         }
-        currentDirectory = nextDirectory;
-        currentFile = filename;
-      }
+        auto objects = opos->bindings;
+        if (std::find(objects.begin(), objects.end(), obj.name) == objects.end()) {
+          LOG(error) << "No object " << obj.name << " in map for task " << taskname;
+          return;
+        }
+        auto nameHash = runtime_hash(obj.name.c_str());
+        InputObjectRoute key{obj.name, nameHash, taskname, hash, policy, sourceType};
+        auto existing = std::find_if(inputObjects->begin(), inputObjects->end(), [&](auto&& x) { return (x.first.uniqueId == nameHash) && (x.first.taskHash == hash); });
+        // If it's the first one, we just add it to the list.
+        if (existing == inputObjects->end()) {
+          obj.count = objh->mPipelineSize;
+          inputObjects->push_back(std::make_pair(key, obj));
+          existing = inputObjects->end() - 1;
+        } else {
+          obj.count = existing->second.count;
+          // Otherwise, we merge it with the existing one.
+          auto merger = existing->second.kind->GetMerge();
+          if (!merger) {
+            LOG(error) << "Already one unmergeable object found for " << obj.name;
+            return;
+          }
+          TList coll;
+          coll.Add(static_cast<TObject*>(obj.obj));
+          merger(existing->second.obj, &coll, nullptr);
+        }
+        // We expect as many objects as the pipeline size, for
+        // a given object name and task hash.
+        existing->second.count -= 1;
 
-      // translate the list-structure created by the registry into a directory structure within the file
-      std::function<void(TList*, TDirectory*)> writeListToFile;
-      writeListToFile = [&](TList* list, TDirectory* parentDir) {
-        TIter next(list);
-        TObject* object = nullptr;
-        while ((object = next())) {
-          if (object->InheritsFrom(TList::Class())) {
-            writeListToFile(static_cast<TList*>(object), parentDir->mkdir(object->GetName(), object->GetName(), true));
-          } else {
-            parentDir->WriteObjectAny(object, object->Class(), object->GetName());
-            auto* written = list->Remove(object);
-            delete written;
+        if (existing->second.count != 0) {
+          return;
+        }
+        // Write the object here.
+        auto route = existing->first;
+        auto entry = existing->second;
+        auto file = ROOTfileNames.find(route.policy);
+        if (file == ROOTfileNames.end()) {
+          return;
+        }
+        auto filename = file->second;
+        if (f[route.policy] == nullptr) {
+          f[route.policy] = TFile::Open(filename.c_str(), "RECREATE");
+        }
+        auto nextDirectory = route.directory;
+        if ((nextDirectory != currentDirectory) || (filename != currentFile)) {
+          if (!f[route.policy]->FindKey(nextDirectory.c_str())) {
+            f[route.policy]->mkdir(nextDirectory.c_str());
           }
+          currentDirectory = nextDirectory;
+          currentFile = filename;
         }
-      };
 
-      TDirectory* currentDir = f[route.policy]->GetDirectory(currentDirectory.c_str());
-      if (route.sourceType == OutputObjSourceType::HistogramRegistrySource) {
-        auto* outputList = static_cast<TList*>(entry.obj);
-        outputList->SetOwner(false);
+        // translate the list-structure created by the registry into a directory structure within the file
+        std::function<void(TList*, TDirectory*)> writeListToFile;
+        writeListToFile = [&](TList* list, TDirectory* parentDir) {
+          TIter next(list);
+          TObject* object = nullptr;
+          while ((object = next())) {
+            if (object->InheritsFrom(TList::Class())) {
+              writeListToFile(static_cast<TList*>(object), parentDir->mkdir(object->GetName(), object->GetName(), true));
+            } else {
+              parentDir->WriteObjectAny(object, object->Class(), object->GetName());
+              auto* written = list->Remove(object);
+              delete written;
+            }
+          }
+        };
+
+        TDirectory* currentDir = f[route.policy]->GetDirectory(currentDirectory.c_str());
+        if (route.sourceType == OutputObjSourceType::HistogramRegistrySource) {
+          auto* outputList = static_cast<TList*>(entry.obj);
+          outputList->SetOwner(false);
+
+          // if registry should live in dedicated folder a TNamed object is appended to the list
+          if (outputList->Last() && outputList->Last()->IsA() == TNamed::Class()) {
+            delete outputList->Last();
+            outputList->RemoveLast();
+            currentDir = currentDir->mkdir(outputList->GetName(), outputList->GetName(), true);
+          }
 
-        // if registry should live in dedicated folder a TNamed object is appended to the list
-        if (outputList->Last() && outputList->Last()->IsA() == TNamed::Class()) {
-          delete outputList->Last();
-          outputList->RemoveLast();
-          currentDir = currentDir->mkdir(outputList->GetName(), outputList->GetName(), true);
+          writeListToFile(outputList, currentDir);
+          outputList->SetOwner();
+          delete outputList;
+          entry.obj = nullptr;
+        } else {
+          currentDir->WriteObjectAny(entry.obj, entry.kind, entry.name.c_str());
+          delete (TObject*)entry.obj;
+          entry.obj = nullptr;
         }
-
-        writeListToFile(outputList, currentDir);
-        outputList->SetOwner();
-        delete outputList;
-        entry.obj = nullptr;
-      } else {
-        currentDir->WriteObjectAny(entry.obj, entry.kind, entry.name.c_str());
-        delete (TObject*)entry.obj;
-        entry.obj = nullptr;
+      };
+      for (int pi = 0; pi < pc.inputs().getNofParts(0); ++pi) {
+        mergePart(pc.inputs().get("x", pi));
       }
     };
   }};