diff --git a/zipline/finance/risk.py b/zipline/finance/risk.py
index a346feb2..144470c2 100644
--- a/zipline/finance/risk.py
+++ b/zipline/finance/risk.py
@@ -396,7 +396,7 @@ class RiskMetricsBase(object):
             "algorithm_period_returns",
             "benchmark_period_returns",
             "excess_return",
-            "trading_days",
+            "num_trading_days",
             "benchmark_volatility",
             "algorithm_volatility",
             "sharpe",