diff --git a/Lib/collections/_defaultdict.py b/Lib/collections/_defaultdict.py
index b9c6c4961..cb9d403c8 100644
--- a/Lib/collections/_defaultdict.py
+++ b/Lib/collections/_defaultdict.py
@@ -17,6 +17,10 @@ class defaultdict(dict):
             val = self.default_factory()
         else:
             raise KeyError(key)
+        # CPython parity: a recursive __missing__ via factory() may have
+        # already populated key; preserve that value instead of overwriting.
+        if key in self:
+            return self[key]
         self[key] = val
         return val
 
diff --git a/Lib/test/test_defaultdict.py b/Lib/test/test_defaultdict.py
index f10603fb4..fbd7354a9 100644
--- a/Lib/test/test_defaultdict.py
+++ b/Lib/test/test_defaultdict.py
@@ -186,7 +186,6 @@ class TestDefaultDict(unittest.TestCase):
         with self.assertRaises(TypeError):
             i |= None
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; AssertionError: 1 != 2
     def test_factory_conflict_with_set_value(self):
         key = "conflict_test"
         count = 0