diff --git a/src/calibre/gui2/pyqt6_compat.py b/src/calibre/gui2/pyqt6_compat.py
index f43f3c4066..da9c2170da 100644
--- a/src/calibre/gui2/pyqt6_compat.py
+++ b/src/calibre/gui2/pyqt6_compat.py
@@ -60,7 +60,7 @@ def set_menu(self, menu):
 # Restore enum values to various classes
 for cls in (
     Qt, QDialog, QToolButton, QAbstractItemView, QDialogButtonBox, QFrame, QComboBox,
-    QLineEdit, QAction, QImage, QIODevice, QPalette, QFormLayout, QEvent
+    QLineEdit, QAction, QImage, QIODevice, QPalette, QFormLayout, QEvent, QMessageBox
 ):
     for var in tuple(vars(cls).values()):
         m = getattr(var, '__members__', {})