diff --git a/tests/test_history.py b/tests/test_history.py
index dc8fc7e1..0ba24146 100644
--- a/tests/test_history.py
+++ b/tests/test_history.py
@@ -351,6 +351,7 @@ def initialize(context):
 
 def handle_data(context, data):
     prices = history(bar_count=2, frequency='1d', field='price')
+    prices['prices_times_two'] = prices[1] * 2
     context.last_prices = prices
 """.strip()
 
diff --git a/zipline/history/history_container.py b/zipline/history/history_container.py
index 4c77a343..51b38562 100644
--- a/zipline/history/history_container.py
+++ b/zipline/history/history_container.py
@@ -443,7 +443,7 @@ class HistoryContainer(object):
         # Get minutes from our buffer panel to build the last row.
         buffer_frame = self.buffer_panel_minutes(
             earliest_minute=self.cur_window_starts[history_spec.frequency],
-        )[field].copy()
+        )[field]
 
         if do_ffill:
             digest_frame = ffill_digest_frame_from_prior_values(
@@ -472,4 +472,9 @@ class HistoryContainer(object):
         else:
             return_frame.ix[algo_dt] = buffer_frame.loc[algo_dt]
 
-        return return_frame
+        # Returning a copy of the DataFrame so that we don't crash if the user
+        # adds columns to the frame.  Ideally we would just drop any added
+        # columns, but pandas 0.12.0 doesn't support in-place dropping of
+        # columns.  We should re-evaluate this implementation once we're on a
+        # more up-to-date pandas.
+        return return_frame.copy()