diff --git a/gtsam/base/treeTraversal-inst.h b/gtsam/base/treeTraversal-inst.h
index a90121738..a8896b45d 100644
--- a/gtsam/base/treeTraversal-inst.h
+++ b/gtsam/base/treeTraversal-inst.h
@@ -113,7 +113,8 @@ namespace gtsam {
           {
             BOOST_FOREACH(const boost::shared_ptr<NODE>& child, node->children)
             {
-              processNode(child, visitorPre(child, myData));
+              DATA childData = visitorPre(child, myData);
+              processNode(child, childData);
             }
           }