diff --git a/src/calibre/gui2/dialogs/data_files_manager.py b/src/calibre/gui2/dialogs/data_files_manager.py
index 3b2db09cdf..282b14b05a 100644
--- a/src/calibre/gui2/dialogs/data_files_manager.py
+++ b/src/calibre/gui2/dialogs/data_files_manager.py
@@ -75,7 +75,7 @@ class Delegate(QStyledItemDelegate):
         if self.doc_size is None:
             d = self.doc_for_index(index)
             self.doc_size = d.size()
-        ans.setHeight(max(self.doc_size.height() + 2, ans.height()))
+        ans.setHeight(max(int(self.doc_size.height() + 2), ans.height()))
         return ans
 
     def paint(self, painter, option, index):