diff --git a/anki/cards.py b/anki/cards.py
index 552df6ddc..c633b114e 100644
--- a/anki/cards.py
+++ b/anki/cards.py
@@ -81,8 +81,9 @@ class Card(object):
         self.mod = intTime()
         self.usn = self.col.usn()
         # bug check
-        if (self.queue == 2 and self.odue):
+        if self.queue == 2 and self.odue:
             warn()
+        assert due < 4294967296
         self.col.db.execute(
             """
 insert or replace into cards values
@@ -109,9 +110,10 @@ insert or replace into cards values
     def flushSched(self):
         self.mod = intTime()
         self.usn = self.col.usn()
-        # bug check
-        if (self.queue == 2 and self.odue):
+        # bug checks
+        if self.queue == 2 and self.odue:
             warn()
+        assert due < 4294967296
         self.col.db.execute(
             """update cards set
 mod=?, usn=?, type=?, queue=?, due=?, ivl=?, factor=?, reps=?,
diff --git a/anki/consts.py b/anki/consts.py
index 094b444e5..11815097a 100644
--- a/anki/consts.py
+++ b/anki/consts.py
@@ -42,7 +42,7 @@ MODEL_STD = 0
 MODEL_CLOZE = 1
 
 # deck schema & syncing vars
-SCHEMA_VERSION = 7
+SCHEMA_VERSION = 8
 SYNC_ZIP_SIZE = int(2.5*1024*1024)
 SYNC_URL = os.environ.get("SYNC_URL") or "https://beta.ankiweb.net/sync/"
 SYNC_VER = 3
diff --git a/anki/storage.py b/anki/storage.py
index c7d13da0a..5c852a549 100644
--- a/anki/storage.py
+++ b/anki/storage.py
@@ -112,6 +112,11 @@ def _upgrade(col, ver):
             "update cards set odue = 0 where (type = 1 or queue = 2) "
             "and not odid")
         col.db.execute("update col set ver = 7")
+    if ver < 8:
+        col.modSchema()
+        col.db.execute(
+            "update cards set due = due / 1000 where due > 4294967296")
+        col.db.execute("update col set ver = 8")
 
 def _upgradeClozeModel(col, m):
     m['type'] = MODEL_CLOZE