diff --git a/test/intervaltree_test.py b/test/intervaltree_test.py
index <HASH>..<HASH> 100644
--- a/test/intervaltree_test.py
+++ b/test/intervaltree_test.py
@@ -94,7 +94,7 @@ def test_duplicate_insert():
     assert len(tree) == 2
     assert tree.items() == contents
 
-    tree.extend([Interval(-10, 20)])
+    tree.extend([Interval(-10, 20), Interval(-10, 20, "arbitrary data")])
     assert len(tree) == 2
     assert tree.items() == contents
made last duplicate insert test be extend() for multiple dups