diff --git a/Lib/test/test_defaultdict.py b/Lib/test/test_defaultdict.py
index a193eb10f16d17..25d7fe21b465c0 100644
--- a/Lib/test/test_defaultdict.py
+++ b/Lib/test/test_defaultdict.py
@@ -186,6 +186,13 @@ def test_union(self):
         with self.assertRaises(TypeError):
             i |= None
 
+        # frozendict
+        i_fd = i | frozendict(s)
+        self.assertIs(type(i_fd), defaultdict)
+        self.assertIs(i_fd.default_factory, int)
+        self.assertDictEqual(i_fd, {1: "one", 2: 2, 0: "zero"})
+        self.assertEqual(list(i_fd), [1, 2, 0])
+
     def test_factory_conflict_with_set_value(self):
         key = "conflict_test"
         count = 0
diff --git a/Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst b/Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst
new file mode 100644
index 00000000000000..cbc94ec065e7db
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst
@@ -0,0 +1,2 @@
+Fix :class:`collections.defaultdict` to work correctly with ``|
+frozendict()``.
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 4ff05727ebc8ce..3171d5cb2ad789 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -2420,7 +2420,7 @@ defdict_or(PyObject* left, PyObject* right)
         self = right;
         other = left;
     }
-    if (!PyDict_Check(other)) {
+    if (!PyAnyDict_Check(other)) {
         Py_RETURN_NOTIMPLEMENTED;
     }
     // Like copy(), this calls the object's class.