diff --git a/sepp/tree.py b/sepp/tree.py
index 7112328..134aaf6 100644
--- a/sepp/tree.py
+++ b/sepp/tree.py
@@ -22,8 +22,6 @@
 
 from dendropy import Tree, Taxon, treecalc
 from dendropy import DataSet as Dataset
-from dendropy.datamodel.treemodel import _convert_node_to_root_polytomy as \
-    convert_node_to_root_polytomy
 from sepp import get_logger, sort_by_value
 from sepp.alignment import get_pdistance
 from sepp.decompose_tree import decompose_by_diameter
@@ -258,7 +256,7 @@ def bipartition_by_edge(self, e):
 
         nr.edge.length = None
         nr.parent_node = None
-        convert_node_to_root_polytomy(nr)
+        nr._convert_node_to_root_polytomy()
         t1 = PhylogeneticTree(Tree(seed_node=nr))
         # temp we could speed this up,
         # by telling the Phylogenetic tree how many leaves it has
diff --git a/setup.py b/setup.py
index 11d9e5e..3be7300 100755
--- a/setup.py
+++ b/setup.py
@@ -162,7 +162,7 @@ def run(self):
       author_email="smirarab@gmail.com, namphuon@cs.utah.edu",
 
       license="General Public License (GPL)",
-      install_requires=["dendropy >= 4.0.0"],
+      install_requires=["dendropy >= 4.6.0"],
       provides=["sepp"],
       scripts=["run_sepp.py", 'run_upp.py', "split_sequences.py"],
       cmdclass={"config": ConfigSepp, "upp": ConfigUPP},