diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index db36248c4ff..3d3bbd7a39a 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -57,10 +57,7 @@
 try:
     from _collections import defaultdict
 except ImportError:
-    # FIXME: try to implement defaultdict in collections.rs rather than in Python
-    # I (coolreader18) couldn't figure out some class stuff with __new__ and
-    # __init__ and __missing__ and subclassing built-in types from Rust, so I went
-    # with this instead.
+    # TODO: RUSTPYTHON - implement defaultdict in Rust
     from ._defaultdict import defaultdict
 
 heapq = None  # Lazily imported
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index b68305dd7aa..0ed51c9f1d8 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -262,7 +262,7 @@ def __contains__(self, key):
         d = c.new_child(b=20, c=30)
         self.assertEqual(d.maps, [{'b': 20, 'c': 30}, {'a': 1, 'b': 2}])
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON
+    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_union_operators(self):
         cm1 = ChainMap(dict(a=1, b=2), dict(c=3, d=4))
         cm2 = ChainMap(dict(a=10, e=5), dict(b=20, d=4))
@@ -1957,7 +1957,7 @@ class X(ByteString): pass
             # No metaclass conflict
             class Z(ByteString, Awaitable): pass
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON; Need to implement __buffer__ and __release_buffer__ (https://docs.python.org/3.13/reference/datamodel.html#emulating-buffer-types)
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; Need to implement __buffer__ and __release_buffer__ (https://docs.python.org/3.13/reference/datamodel.html#emulating-buffer-types)
     def test_Buffer(self):
         for sample in [bytes, bytearray, memoryview]:
             self.assertIsInstance(sample(b"x"), Buffer)
@@ -2029,7 +2029,7 @@ def insert(self, index, value):
         self.assertEqual(len(mss), len(mss2))
         self.assertEqual(list(mss), list(mss2))
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON
+    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_illegal_patma_flags(self):
         with self.assertRaises(TypeError):
             class Both(Collection):
@@ -2121,6 +2121,19 @@ def test_basics(self):
         self.assertEqual(c.setdefault('e', 5), 5)
         self.assertEqual(c['e'], 5)
 
+    def test_update_reentrant_add_clears_counter(self):
+        c = Counter()
+        key = object()
+
+        class Evil(int):
+            def __add__(self, other):
+                c.clear()
+                return NotImplemented
+
+        c[key] = Evil()
+        c.update([key])
+        self.assertEqual(c[key], 1)
+
     def test_init(self):
         self.assertEqual(list(Counter(self=42).items()), [('self', 42)])
         self.assertEqual(list(Counter(iterable=42).items()), [('iterable', 42)])