diff --git a/qt/aqt/reviewer.py b/qt/aqt/reviewer.py
index 322a62ad0..6f4d9fdeb 100644
--- a/qt/aqt/reviewer.py
+++ b/qt/aqt/reviewer.py
@@ -154,6 +154,7 @@ class Reviewer:
         self._card_info = ReviewerCardInfo(self.mw)
         self._previous_card_info = PreviousReviewerCardInfo(self.mw)
         self._states_mutated = True
+        self._state_mutation_js = None
         self._reps: int = None
         self._show_question_timer: QTimer | None = None
         self._show_answer_timer: QTimer | None = None