diff --git a/tests/test_sources.py b/tests/test_sources.py
index 10ad80ec..506887e1 100644
--- a/tests/test_sources.py
+++ b/tests/test_sources.py
@@ -53,8 +53,8 @@ class TestDataFrameSource(TestCase):
         for event in source:
             self.assertTrue('sid' in event)
             self.assertTrue('arbitrary' in event)
-            self.assertTrue('volume' in event)
-            self.assertTrue('price' in event)
+            self.assertTrue(hasattr(event, 'volume'))
+            self.assertTrue(hasattr(event, 'price'))
             self.assertEquals(event['arbitrary'], 1.)
             self.assertEquals(event['sid'], 0)
             self.assertTrue(isinstance(event['volume'], int))
diff --git a/zipline/transforms/returns.py b/zipline/transforms/returns.py
index 401a9cda..4a9f750d 100644
--- a/zipline/transforms/returns.py
+++ b/zipline/transforms/returns.py
@@ -96,7 +96,7 @@ class ReturnsFromPriorClose(object):
         We only allow events with a price field to be run through
         the returns transform.
         """
-        if 'price' not in event:
+        if not hasattr(event, 'price'):
             raise WrongDataForTransform(
                 transform="ReturnsEventWindow",
                 fields=['price'])
diff --git a/zipline/transforms/utils.py b/zipline/transforms/utils.py
index fe2bf625..fa4b3f58 100644
--- a/zipline/transforms/utils.py
+++ b/zipline/transforms/utils.py
@@ -280,7 +280,7 @@ class EventWindow(with_metaclass(ABCMeta)):
         We only allow events with all of our tracked fields.
         """
         # All events require a 'dt' field.
-        if 'dt' not in event:
+        if not hasattr(event, 'dt'):
             raise WrongDataForTransform(
                 transform=self.__class__.__name__,
                 fields=['dt'],