diff --git a/gtsam/discrete/DecisionTree-inl.h b/gtsam/discrete/DecisionTree-inl.h
index 99f29b8e5..ffb8d7c69 100644
--- a/gtsam/discrete/DecisionTree-inl.h
+++ b/gtsam/discrete/DecisionTree-inl.h
@@ -39,10 +39,10 @@
 #include <string>
 #include <vector>
 
-using boost::assign::operator+=;
-
 namespace gtsam {
 
+  using boost::assign::operator+=;
+
   /****************************************************************************/
   // Node
   /****************************************************************************/