From 2a4c97a5795923e845257be49eb881df7de5aae8 Mon Sep 17 00:00:00 2001
From: uttam12331 <uttam12331@users.noreply.github.com>
Date: Wed, 5 Aug 2026 01:07:00 +0530
Subject: [PATCH 1/2] Unpack the single type arg for Counter keys when
 unstructuring

`mapping_unstructure_factory`'s single-type-arg branch ("Probably a Counter")
assigned the whole `args` tuple to `key_arg`, then passed it to
`get_unstructure_hook`, which expects a single type. As a result the key hook
was resolved for `(KeyType,)` (falling back to identity) instead of
`KeyType`, so Counter keys that need real unstructuring were left unchanged.

Unpack `args[0]`, matching the structure factory's `(key_type,) = args`, and
add a regression test.
---
 src/cattrs/gen/__init__.py            |  2 +-
 tests/test_unstructure_collections.py | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/cattrs/gen/__init__.py b/src/cattrs/gen/__init__.py
index b7873ab4..f558b1f6 100644
--- a/src/cattrs/gen/__init__.py
+++ b/src/cattrs/gen/__init__.py
@@ -1029,7 +1029,7 @@ def mapping_unstructure_factory(
             key_arg, val_arg = args
         else:
             # Probably a Counter
-            key_arg, val_arg = args, Any
+            key_arg, val_arg = args[0], Any
         # We can do the dispatch here and now.
         kh = key_handler or converter.get_unstructure_hook(key_arg, cache_result=False)
         if kh == identity:
diff --git a/tests/test_unstructure_collections.py b/tests/test_unstructure_collections.py
index 6654c889..03bd2431 100644
--- a/tests/test_unstructure_collections.py
+++ b/tests/test_unstructure_collections.py
@@ -148,3 +148,23 @@ def test_collection_unstructure_override_mapping():
     assert c.unstructure({1: 2}) == Map({1: 2})
     assert c.unstructure({1: 2}, unstructure_as=MutableMapping[int, int]) == Map({1: 2})
     assert c.unstructure({1: 2}, unstructure_as=Mapping[int, int]) == Map({1: 2})
+
+
+def test_counter_unstructure_applies_key_hook():
+    """Counter keys must be unstructured with the key type's own hook.
+
+    Regression: the single-type-arg ("Probably a Counter") branch assigned the
+    whole ``args`` tuple to ``key_arg``, so the key hook was resolved for
+    ``(KeyType,)`` (falling back to identity) instead of ``KeyType``, leaving
+    keys un-unstructured.
+    """
+
+    @define(frozen=True)
+    class Key:
+        v: int
+
+    c = Converter()
+    c.register_unstructure_hook(Key, lambda k: k.v)
+
+    result = c.unstructure(Counter({Key(1): 5, Key(2): 3}), unstructure_as=Counter[Key])
+    assert result == {1: 5, 2: 3}

From cca9472641ad9a57d90ae70094b8324177aa665d Mon Sep 17 00:00:00 2001
From: uttam12331 <uttam12331@users.noreply.github.com>
Date: Wed, 5 Aug 2026 01:07:46 +0530
Subject: [PATCH 2/2] Add HISTORY entry for Counter key unstructure fix (#768)

---
 HISTORY.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/HISTORY.md b/HISTORY.md
index 07b1c970..2120900a 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -13,6 +13,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
 
 ## NEXT (UNRELEASED)
 
+- Fix `Counter` keys not being unstructured with the key type's own hook; the single-type-arg branch passed the whole type-args tuple to the key hook lookup instead of the key type.
+  ([#768](https://github.com/python-attrs/cattrs/pull/768))
 - Fix `create_default_dis_func <cattrs.disambiguators.create_default_dis_func>` (aka `create_uniq_field_dis_func`) failing to disambiguate valid unions depending on the order of the member classes; unique fields are now resolved iteratively to a fixpoint.
   ([#230](https://github.com/python-attrs/cattrs/issues/230) [#765](https://github.com/python-attrs/cattrs/pull/765))
 - Support more recursive types on 3.14+ with specialized factories for [`annotationlib.ForwardRef`](https://docs.python.org/3/library/annotationlib.html#annotationlib.ForwardRef).