diff --git a/flashcards/serializers.py b/flashcards/serializers.py
index 168bd84..3eeda01 100644
--- a/flashcards/serializers.py
+++ b/flashcards/serializers.py
@@ -95,11 +95,11 @@ class MaskFieldSerializer(serializers.Field):
         return dumps(list(self._make_mask(value)))
 
     def to_internal_value(self, value):
-        return self._make_mask(value)
+        return self._make_mask(loads(value))
 
     def _make_mask(self, data):
         try:
-            mask = FlashcardMask(loads(data))
+            mask = FlashcardMask(data)
         except ValueError:
             raise serializers.ValidationError("Invalid JSON for MaskField")
         except TypeError:
diff --git a/flashcards/validators.py b/flashcards/validators.py
index 81d8417..1620eef 100644
--- a/flashcards/validators.py
+++ b/flashcards/validators.py
@@ -4,8 +4,9 @@ from collections import Iterable
 
 
 class FlashcardMask(set):
-    def __init__(self, *args, **kwargs):
-        super(FlashcardMask, self).__init__(*args, **kwargs)
+    def __init__(self, iterable, *args, **kwargs):
+        iterable = map(tuple, iterable)
+        super(FlashcardMask, self).__init__(iterable, *args, **kwargs)
         self._iterable_check()
         self._interval_check()
         self._overlap_check()