diff --git a/GUI/Model/Files/DatafilesSet.cpp b/GUI/Model/Files/DatafilesSet.cpp
index 682d89db3e71cdf024425854b0d1a9a96ea5c61a..6bcaed4366b6ccbabd86549fcef67f1eca8e32b9 100644
--- a/GUI/Model/Files/DatafilesSet.cpp
+++ b/GUI/Model/Files/DatafilesSet.cpp
@@ -97,7 +97,7 @@ void DatafilesSet::readFrom(QXmlStreamReader* r)
         throw std::runtime_error(r->errorString().toLatin1());
 }
 
-void DatafilesSet::writeDatafiles(const QString& projectDir)
+void DatafilesSet::writeDatafiles(const QString& projectDir) const
 {
     for (const auto* dfile_item : dfileItems())
         dfile_item->writeDatafiles(projectDir);
diff --git a/GUI/Model/Files/DatafilesSet.h b/GUI/Model/Files/DatafilesSet.h
index a5db50471375ac761ebcbab53b419007ca6cb438..36bc2693bcc0bbb83fde946eb26f4cd9f02ec3ad 100644
--- a/GUI/Model/Files/DatafilesSet.h
+++ b/GUI/Model/Files/DatafilesSet.h
@@ -47,7 +47,7 @@ public:
 private:
     QVector<DataItem*> dataItems() const;
 
-    DatafilesCleaner dataFilesCleaner;
+    mutable DatafilesCleaner dataFilesCleaner;
     std::vector<std::unique_ptr<DatafileItem>> m_dfile_items;
     int m_current_index = -1;
 };