diff --git a/tests/test_algorithm.py b/tests/test_algorithm.py
index bc82f310..4e9735d0 100644
--- a/tests/test_algorithm.py
+++ b/tests/test_algorithm.py
@@ -331,27 +331,27 @@ class TestMiscellaneousAPI(TestCase):
         algo = TradingAlgorithm(asset_metadata=metadata)
 
         # Test before either PLAY existed
-        algo.datetime = pd.Timestamp('2001-12-01', tz='UTC')
+        algo.sim_params.period_end = pd.Timestamp('2001-12-01', tz='UTC')
         with self.assertRaises(SymbolNotFound):
             algo.symbol('PLAY')
         with self.assertRaises(SymbolNotFound):
             algo.symbols('PLAY')
 
         # Test when first PLAY exists
-        algo.datetime = pd.Timestamp('2002-12-01', tz='UTC')
+        algo.sim_params.period_end = pd.Timestamp('2002-12-01', tz='UTC')
         list_result = algo.symbols('PLAY')
         self.assertEqual(0, list_result[0])
 
         # Test after first PLAY ends
-        algo.datetime = pd.Timestamp('2004-12-01', tz='UTC')
+        algo.sim_params.period_end = pd.Timestamp('2004-12-01', tz='UTC')
         self.assertEqual(0, algo.symbol('PLAY'))
 
         # Test after second PLAY begins
-        algo.datetime = pd.Timestamp('2005-12-01', tz='UTC')
+        algo.sim_params.period_end = pd.Timestamp('2005-12-01', tz='UTC')
         self.assertEqual(1, algo.symbol('PLAY'))
 
         # Test after second PLAY ends
-        algo.datetime = pd.Timestamp('2006-12-01', tz='UTC')
+        algo.sim_params.period_end = pd.Timestamp('2006-12-01', tz='UTC')
         self.assertEqual(1, algo.symbol('PLAY'))
         list_result = algo.symbols('PLAY')
         self.assertEqual(1, list_result[0])
diff --git a/zipline/algorithm.py b/zipline/algorithm.py
index 11dc7147..0403c1ef 100644
--- a/zipline/algorithm.py
+++ b/zipline/algorithm.py
@@ -695,7 +695,8 @@ class TradingAlgorithm(object):
         """
         return self.asset_finder.lookup_symbol_resolve_multiple(
             symbol_str,
-            as_of_date=self.datetime)
+            as_of_date=self.sim_params.period_end
+        )
 
     @api_method
     def symbols(self, *args):