diff --git a/zipline/finance/trading.py b/zipline/finance/trading.py
index 0d003326..b7ed09c8 100644
--- a/zipline/finance/trading.py
+++ b/zipline/finance/trading.py
@@ -196,7 +196,7 @@ class TradingEnvironment(object):
             .write_all(self.engine, allow_sid_assignment=allow_sid_assignment)
 
     def _write_data_dicts(self, equities=None, futures=None, exchanges=None,
-                          root_symbols=None, allow_sid_assignment=True):
+                          root_symbols=None):
         AssetDBWriterFromDictionary(equities, futures, exchanges, root_symbols)\
             .write_all(self.engine)