diff --git a/flashcards/serializers.py b/flashcards/serializers.py
index d97e0f6..e36527e 100644
--- a/flashcards/serializers.py
+++ b/flashcards/serializers.py
@@ -102,7 +102,9 @@ class MaskFieldSerializer(serializers.Field):
         return dumps(list(self._make_mask(value)))
 
     def to_internal_value(self, value):
-        return self._make_mask(loads(value))
+        if not isinstance(value, list):
+            value = loads(value)
+        return self._make_mask(value)
 
     def _make_mask(self, data):
         try:
@@ -239,7 +241,7 @@ class QuizAnswerRequestSerializer(ModelSerializer):
     correct = BooleanField(required=False, help_text="The user's self-evaluation of their response")
 
     def __init__(self, instance=None, data=empty, **kwargs):
-        assert isinstance(instance, UserFlashcardQuiz)
+        assert isinstance(instance, UserFlashcardQuiz) or instance is None
         super(QuizAnswerRequestSerializer, self).__init__(instance=instance, data=data, **kwargs)
 
     def validate_response(self, response):
diff --git a/flashcards/views.py b/flashcards/views.py
index 2e4e750..fb1194a 100644
--- a/flashcards/views.py
+++ b/flashcards/views.py
@@ -374,6 +374,7 @@ class UserFlashcardQuizViewSet(GenericViewSet, CreateModelMixin, UpdateModelMixi
             raise ValidationError("No matching flashcard found in your decks")
 
         user_flashcard = user_flashcard_filter.order_by('?').first()
+        # user_flashcard = user_flashcard_filter.annotate(spaced=F())
         mask = user_flashcard.get_mask().get_random_blank()
         user_flashcard_quiz = UserFlashcardQuiz(user_flashcard=user_flashcard,
                                                 blanked_word=user_flashcard.flashcard.text[slice(*mask)])