diff --git a/taxoniumtools/src/taxoniumtools/ushertools.py b/taxoniumtools/src/taxoniumtools/ushertools.py
index 33a0dd2f..94e1c774 100644
--- a/taxoniumtools/src/taxoniumtools/ushertools.py
+++ b/taxoniumtools/src/taxoniumtools/ushertools.py
@@ -197,13 +197,14 @@ def prune_node(self, node_to_prune):
                             clade_type] == "":
                         child.clades[clade_type] = clade_annotation
             grandparent = parent.parent
-            grandparent.remove_child(parent)
             parent.remove_child(child)
-            grandparent.add_child(child)
+            if grandparent:
+                grandparent.remove_child(parent)
+                grandparent.add_child(child)
 
     def shear_tree(self, theshold=1000):
         """Consider each node. If at any point a child has fewer than 1/threshold proportion of the num_tips, then prune it"""
-        for node in alive_it(self.tree.traverse_postorder()):
+        for node in alive_it(list(self.tree.traverse_postorder())):
             if len(node.children) > 1:
                 total_tips = node.num_tips
                 for child in node.children: