diff --git a/anki/cards.py b/anki/cards.py
index 5e455899f..5034bc3fd 100644
--- a/anki/cards.py
+++ b/anki/cards.py
@@ -70,6 +70,8 @@ class Card(object):
     def flush(self):
         self.mod = intTime()
         self.usn = self.col.usn()
+        # bug check
+        assert not (self.queue == 2 and self.odue)
         self.col.db.execute(
             """
 insert or replace into cards values
@@ -96,6 +98,8 @@ insert or replace into cards values
     def flushSched(self):
         self.mod = intTime()
         self.usn = self.col.usn()
+        # bug check
+        assert not (self.queue == 2 and self.odue)
         self.col.db.execute(
             """update cards set
 mod=?, usn=?, type=?, queue=?, due=?, ivl=?, factor=?, reps=?,