diff --git a/zipline/utils/factory.py b/zipline/utils/factory.py
index 1a83a793..79c04333 100644
--- a/zipline/utils/factory.py
+++ b/zipline/utils/factory.py
@@ -101,7 +101,7 @@ def create_random_simulation_parameters():
 
         random_index = random.randint(
             0,
-            len(treasury_curves)
+            len(treasury_curves) - 1
         )
 
         start_dt = treasury_curves.keys()[random_index]