diff --git a/requirements.txt b/requirements.txt
index b604a47..babd7ba 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,7 +4,6 @@ requests>=2.31
 multitasking>=0.0.7
 platformdirs>=2.0.0
 pytz>=2022.5
-frozendict>=2.3.4
 beautifulsoup4>=4.11.1
 lxml>=4.9.0
 peewee>=3.16.2
diff --git a/setup.py b/setup.py
index cbe04b7..ab6bf36 100644
--- a/setup.py
+++ b/setup.py
@@ -62,7 +62,7 @@ setup(
     install_requires=['pandas>=1.3.0', 'numpy>=1.16.5',
                       'requests>=2.31', 'multitasking>=0.0.7',
                       'platformdirs>=2.0.0', 'pytz>=2022.5',
-                      'frozendict>=2.3.4', 'peewee>=3.16.2',
+                      'peewee>=3.16.2',
                       'beautifulsoup4>=4.11.1', 'curl_cffi>=0.15',
                       'protobuf>=3.19.0', 'websockets>=13.0'],
     extras_require={
diff --git a/tests/test_data.py b/tests/test_data.py
new file mode 100644
index 0000000..d0867e4
--- /dev/null
+++ b/tests/test_data.py
@@ -0,0 +1,53 @@
+"""Tests for yfinance.data internal helpers."""
+import unittest
+from functools import lru_cache
+
+from yfinance.data import lru_cache_freezeargs
+from yfinance.utils import frozendict
+
+
+class TestFrozenDict(unittest.TestCase):
+    def test_is_dict_subclass(self):
+        d = frozendict({"a": 1, "b": 2})
+        self.assertEqual(d["a"], 1)
+        self.assertEqual(d.get("b"), 2)
+        self.assertEqual(set(d.keys()), {"a", "b"})
+        self.assertIsInstance(d, dict)
+
+    def test_is_hashable(self):
+        d1 = frozendict({"a": 1, "b": 2})
+        d2 = frozendict({"b": 2, "a": 1})
+        self.assertEqual(hash(d1), hash(d2))
+        self.assertEqual(len({d1, d2}), 1)
+
+    def test_mutation_raises(self):
+        d = frozendict({"a": 1})
+        with self.assertRaises(TypeError):
+            d["b"] = 2
+        with self.assertRaises(TypeError):
+            del d["a"]
+        with self.assertRaises(AttributeError):
+            d.pop("a")
+        with self.assertRaises(AttributeError):
+            d.clear()
+        with self.assertRaises(AttributeError):
+            d.update({"x": 9})
+
+    def test_lru_cache_integration(self):
+        call_count = {"n": 0}
+
+        @lru_cache_freezeargs
+        @lru_cache(maxsize=8)
+        def fn(params):
+            call_count["n"] += 1
+            return sum(params.values())
+
+        self.assertEqual(fn({"a": 1, "b": 2}), 3)
+        self.assertEqual(fn({"a": 1, "b": 2}), 3)
+        self.assertEqual(call_count["n"], 1)
+        self.assertEqual(fn({"a": 1, "b": 3}), 4)
+        self.assertEqual(call_count["n"], 2)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/yfinance/data.py b/yfinance/data.py
index 5f2a9ba..693084b 100644
--- a/yfinance/data.py
+++ b/yfinance/data.py
@@ -9,9 +9,8 @@ from urllib.parse import urlsplit, urljoin
 from bs4 import BeautifulSoup
 import datetime
 
-from frozendict import frozendict
-
 from . import utils, cache
+from .utils import frozendict
 from .config import YfConfig
 import threading
 
diff --git a/yfinance/utils.py b/yfinance/utils.py
index 3db289f..99de06d 100644
--- a/yfinance/utils.py
+++ b/yfinance/utils.py
@@ -43,6 +43,34 @@ from yfinance import const
 from yfinance.exceptions import YFException
 from yfinance.config import YfConfig
 
+# Use the third-party ``frozendict`` package if installed; otherwise fall
+# back to a small pure-Python equivalent (PEP 814).
+try:
+    from frozendict import frozendict  # type: ignore[import-not-found]
+except ImportError:
+    class frozendict(dict):  # type: ignore[no-redef]
+        """Hashable, read-only ``dict`` used as an ``lru_cache`` key."""
+        __slots__ = ()
+
+        def __hash__(self):  # type: ignore[override]
+            return hash(frozenset(self.items()))
+
+        def __setitem__(self, *args, **kwargs):
+            raise TypeError(f"'{type(self).__name__}' object doesn't support item assignment")
+
+        def __delitem__(self, *args, **kwargs):
+            raise TypeError(f"'{type(self).__name__}' object doesn't support item deletion")
+
+        def _readonly(self, *args, **kwargs):
+            raise AttributeError(f"'{type(self).__name__}' object is read-only")
+
+        pop = _readonly  # type: ignore[assignment]
+        popitem = _readonly  # type: ignore[assignment]
+        clear = _readonly  # type: ignore[assignment]
+        update = _readonly  # type: ignore[assignment]
+        setdefault = _readonly  # type: ignore[assignment]
+
+
 # From https://stackoverflow.com/a/59128615
 def attributes(obj):
     disallowed_names = {