diff --git a/dataset/persistence/util.py b/dataset/persistence/util.py
index 9a6b8fe..b41ef29 100644
--- a/dataset/persistence/util.py
+++ b/dataset/persistence/util.py
@@ -72,11 +72,15 @@ def sqlite_datetime_fix():
         epoch = datetime(1970, 1, 1, 0, 0, 0)
 
         def process_bind_param(self, value, dialect):
+            if value is None:
+                return None
             if isinstance(value, datetime):
                 return value
             return (value / 1000 - self.epoch).total_seconds()
 
         def process_result_value(self, value, dialect):
+            if value is None:
+                return None
             if isinstance(value, int):
                 return self.epoch + timedelta(seconds=value / 1000)
             return value