diff --git a/src/calibre/gui2/dialogs/check_library.py b/src/calibre/gui2/dialogs/check_library.py
index 56905caece..0625b7eef7 100644
--- a/src/calibre/gui2/dialogs/check_library.py
+++ b/src/calibre/gui2/dialogs/check_library.py
@@ -44,7 +44,7 @@ class DBCheck(QDialog):  # {{{
         self.rejected = False
 
     def start(self):
-        t = self.thread = Thread(target=self.vacuum, daemon=True)
+        t = self.thread = Thread(target=self.vacuum, daemon=True, name='VacuumDB')
         t.start()
 
     def vacuum(self):
diff --git a/src/calibre/gui2/library/models.py b/src/calibre/gui2/library/models.py
index 086a009209..75d764ec4a 100644
--- a/src/calibre/gui2/library/models.py
+++ b/src/calibre/gui2/library/models.py
@@ -312,7 +312,7 @@ class BooksModel(QAbstractTableModel):  # {{{
             if font_type != 'normal':
                 self.styled_columns[colname] = getattr(self, f'{font_type}_font')
                 old[colname] = font_type
-            self.db.new_api.set_pref('styled_columns', old)
+            db.set_pref('styled_columns', old)
             col = self.column_map.index(colname)
             for row in range(self.rowCount(QModelIndex())):
                 self.dataChanged.emit(self.index(row, col), self.index(row,