diff --git a/chainladder/methods/benktander.py b/chainladder/methods/benktander.py
index 44c347cb..6f7b3b20 100644
--- a/chainladder/methods/benktander.py
+++ b/chainladder/methods/benktander.py
@@ -66,7 +66,7 @@ def fit(self, X, y=None, sample_weight=None):
         return self
 
     def _get_ultimate_(self, X, sample_weight, obj):
-        ult = obj.X_
+        ult = copy.copy(obj.X_)
         origin, development = -2, -1  # Set axes by name
         latest = X.latest_diagonal.values
         apriori = sample_weight.values*self.apriori