diff --git a/src/akonadi/akonadidatasourcequeries.h b/src/akonadi/akonadidatasourcequeries.h
--- a/src/akonadi/akonadidatasourcequeries.h
+++ b/src/akonadi/akonadidatasourcequeries.h
@@ -41,7 +41,7 @@
     typedef Domain::QueryResultProvider<Domain::DataSource::Ptr> DataSourceProvider;
     typedef Domain::QueryResult<Domain::DataSource::Ptr> DataSourceResult;
 
-    DataSourceQueries(const StorageInterface::FetchContentTypes &contentTypes,
+    DataSourceQueries(StorageInterface::FetchContentTypes contentTypes,
                       const StorageInterface::Ptr &storage,
                       const SerializerInterface::Ptr &serializer,
                       const MonitorInterface::Ptr &monitor);
diff --git a/src/akonadi/akonadidatasourcequeries.cpp b/src/akonadi/akonadidatasourcequeries.cpp
--- a/src/akonadi/akonadidatasourcequeries.cpp
+++ b/src/akonadi/akonadidatasourcequeries.cpp
@@ -28,7 +28,7 @@
 
 using namespace Akonadi;
 
-DataSourceQueries::DataSourceQueries(const StorageInterface::FetchContentTypes &contentTypes,
+DataSourceQueries::DataSourceQueries(StorageInterface::FetchContentTypes contentTypes,
                                      const StorageInterface::Ptr &storage,
                                      const SerializerInterface::Ptr &serializer,
                                      const MonitorInterface::Ptr &monitor)
diff --git a/src/presentation/querytreemodelbase.h b/src/presentation/querytreemodelbase.h
--- a/src/presentation/querytreemodelbase.h
+++ b/src/presentation/querytreemodelbase.h
@@ -100,7 +100,7 @@
                                 QObject *parent = Q_NULLPTR);
     virtual QMimeData *createMimeData(const QModelIndexList &indexes) const = 0;
     QueryTreeNodeBase *nodeFromIndex(const QModelIndex &index) const;
-    void setRootIndexFlag(const Qt::ItemFlags &flags);
+    void setRootIndexFlag(Qt::ItemFlags flags);
 
 private:
     friend class QueryTreeNodeBase;
diff --git a/src/presentation/querytreemodelbase.cpp b/src/presentation/querytreemodelbase.cpp
--- a/src/presentation/querytreemodelbase.cpp
+++ b/src/presentation/querytreemodelbase.cpp
@@ -242,7 +242,7 @@
     return index.isValid() ? static_cast<QueryTreeNodeBase*>(index.internalPointer()) : m_rootNode;
 }
 
-void QueryTreeModelBase::setRootIndexFlag(const Qt::ItemFlags &flags)
+void QueryTreeModelBase::setRootIndexFlag(Qt::ItemFlags flags)
 {
     m_rootIndexFlag = flags;
 }