diff --git a/taxoniumtools/src/taxoniumtools/ushertools.py b/taxoniumtools/src/taxoniumtools/ushertools.py
index 908fa66b..b353d756 100644
--- a/taxoniumtools/src/taxoniumtools/ushertools.py
+++ b/taxoniumtools/src/taxoniumtools/ushertools.py
@@ -180,7 +180,7 @@ def preorder_traversal_internal(node):
     yield node
     for clade in node.children:
         for x in preorder_traversal_internal(clade):
-            if not x.children:
+            if not x.is_leaf():
                 yield x