diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index 530c536c..89e89561 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -4,6 +4,10 @@ MontePy Changelog
 #Next Version#
 --------------
 
+**Bug Fixes**
+
+* Fixed a bug where ``problem.materials.append_renumber`` would double add a material to ``problem.data_inputs`` (:issue:`516`).
+
 **Performance Improvement**
 
 * Fixed method of linking ``Material`` to ``ThermalScattering`` objects, avoiding a very expensive O(N:sup:`2`) (:issue:`510`).
diff --git a/montepy/numbered_object_collection.py b/montepy/numbered_object_collection.py
index e542c82e..bbbd49d3 100644
--- a/montepy/numbered_object_collection.py
+++ b/montepy/numbered_object_collection.py
@@ -439,6 +439,7 @@ def append(self, obj, insert_in_data=True):
         :type insert_in_data: bool
         :raises NumberConflictError: if this object has a number that is already in use.
         """
+        super().append(obj)
         if self._problem:
             if self._last_index:
                 index = self._last_index
@@ -452,7 +453,6 @@ def append(self, obj, insert_in_data=True):
             if insert_in_data:
                 self._problem.data_inputs.insert(index + 1, obj)
             self._last_index = index + 1
-        super().append(obj)
 
     def __delitem__(self, idx):
         if not isinstance(idx, int):
diff --git a/tests/test_numbered_collection.py b/tests/test_numbered_collection.py
index f88cf831..d5a43f9e 100644
--- a/tests/test_numbered_collection.py
+++ b/tests/test_numbered_collection.py
@@ -317,11 +317,13 @@ def test_data_append(cp_simple_problem):
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
     # trigger getting data_inputs end
     prob.materials.clear()
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
     prob.data_inputs.clear()
     prob.materials._last_index = None
     new_mat = copy.deepcopy(next(iter(prob.materials)))
@@ -329,6 +331,7 @@ def test_data_append(cp_simple_problem):
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
     # trigger getting index of last material
     prob.materials._last_index = None
     new_mat = copy.deepcopy(next(iter(prob.materials)))
@@ -336,6 +339,16 @@ def test_data_append(cp_simple_problem):
     prob.materials.append(new_mat)
     assert new_mat in prob.materials
     assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
+
+
+def test_data_append_renumber(cp_simple_problem):
+    prob = cp_simple_problem
+    new_mat = copy.deepcopy(next(iter(prob.materials)))
+    prob.materials.append_renumber(new_mat)
+    assert new_mat in prob.materials
+    assert new_mat in prob.data_inputs
+    assert prob.data_inputs.count(new_mat) == 1
 
 
 def test_data_remove(cp_simple_problem):