diff --git a/src/python.rs b/src/python.rs
index 2cc8585..daa4259 100644
--- a/src/python.rs
+++ b/src/python.rs
@@ -272,7 +272,7 @@ impl Taxonomy {
         py_try!(newick::save(
             &mut bytes,
             &self.tax,
-            Some(TaxonomyTrait::<InternalIndex>::root(&self.tax))
+            Some(TaxonomyTrait::<&str>::root(&self.tax))
         ));
         Ok(PyBytes::new(py, &bytes).into())
     }
diff --git a/test_python.py b/test_python.py
index 034a71f..1a2a1cf 100644
--- a/test_python.py
+++ b/test_python.py
@@ -278,6 +278,12 @@ def test_can_clone(self):
         self.assertIsNotNone(tax2.node("E"))
         self.assertEqual(len(tax2), 6)
 
+    def test_output_uses_tax_ids(self):
+        res = self.tax.to_newick().decode("utf-8")
+
+        for tax_id in ["A", "B", "C", "D", "E", "F"]:
+            assert tax_id in res
+
 
 class NCBITestCase(unittest.TestCase):
     def _create_tax(self):