diff --git a/stdlib/@tests/test_cases/builtins/check_frozendict-py315.py b/stdlib/@tests/test_cases/builtins/check_frozendict-py315.py
index dd222a4c796f..ec96ff5b2853 100644
--- a/stdlib/@tests/test_cases/builtins/check_frozendict-py315.py
+++ b/stdlib/@tests/test_cases/builtins/check_frozendict-py315.py
@@ -13,3 +13,17 @@
     assert_type(frozendict({"x": 1}), frozendict[str, int])
     assert_type(frozendict([("k", 2)]), frozendict[str, int])
     assert_type(frozendict({"x": 1}, y=2), frozendict[str, int])
+
+    # gh-16668: like ``Mapping``, ``frozendict`` is covariant in its value type
+    # (but not in its key type).
+    def takes_optional_values(d: frozendict[str, int | None]) -> None: ...
+
+    int_values: frozendict[str, int] = frozendict(a=1)
+    takes_optional_values(int_values)
+    assert_type(int_values.get("a"), int | None)
+    assert_type(int_values.get("a", 0), int)
+    assert_type(int_values.get("a", "x"), int | str)
+
+    def takes_object_keys(d: frozendict[object, int]) -> None: ...
+
+    takes_object_keys(int_values)  # type: ignore
diff --git a/stdlib/builtins.pyi b/stdlib/builtins.pyi
index 0075adf561c2..1628f1bbf760 100644
--- a/stdlib/builtins.pyi
+++ b/stdlib/builtins.pyi
@@ -78,6 +78,7 @@ _T_contra = TypeVar("_T_contra", contravariant=True)
 _R_co = TypeVar("_R_co", covariant=True)
 _KT = TypeVar("_KT")
 _VT = TypeVar("_VT")
+_VT_co = TypeVar("_VT_co", covariant=True)
 _S = TypeVar("_S")
 _T1 = TypeVar("_T1")
 _T2 = TypeVar("_T2")
@@ -1378,7 +1379,7 @@ class dict(MutableMapping[_KT, _VT]):
 
 if sys.version_info >= (3, 15):
     @disjoint_base
-    class frozendict(Mapping[_KT, _VT]):
+    class frozendict(Mapping[_KT, _VT_co]):
         @overload
         def __new__(cls, /) -> frozendict[Any, Any]: ...
         @overload
@@ -1396,7 +1397,7 @@ if sys.version_info >= (3, 15):
             cls: type[frozendict[str, _VT]], iterable: Iterable[tuple[str, _VT]], /, **kwargs: _VT
         ) -> frozendict[str, _VT]: ...
 
-        def copy(self) -> frozendict[_KT, _VT]: ...
+        def copy(self) -> frozendict[_KT, _VT_co]: ...
 
         @overload
         @classmethod
@@ -1406,27 +1407,27 @@ if sys.version_info >= (3, 15):
         def fromkeys(cls, iterable: Iterable[_T], value: _S, /) -> frozendict[_T, _S]: ...
 
         @overload  # type: ignore[override]
-        def get(self, key: _KT, default: None = None, /) -> _VT | None: ...
+        def get(self, key: _KT, default: None = None, /) -> _VT_co | None: ...
         @overload
-        def get(self, key: _KT, default: _VT, /) -> _VT: ...
+        def get(self, key: _KT, default: _VT_co, /) -> _VT_co: ...  # type: ignore[misc] # pyright: ignore[reportGeneralTypeIssues] # Covariant type as parameter  # pyrefly: ignore [invalid-variance]
         @overload
-        def get(self, key: _KT, default: _T, /) -> _VT | _T: ...
+        def get(self, key: _KT, default: _T, /) -> _VT_co | _T: ...
 
-        def keys(self) -> dict_keys[_KT, _VT]: ...
-        def values(self) -> dict_values[_KT, _VT]: ...
-        def items(self) -> dict_items[_KT, _VT]: ...
+        def keys(self) -> dict_keys[_KT, _VT_co]: ...
+        def values(self) -> dict_values[_KT, _VT_co]: ...
+        def items(self) -> dict_items[_KT, _VT_co]: ...
         def __len__(self) -> int: ...
-        def __getitem__(self, key: _KT, /) -> _VT: ...
+        def __getitem__(self, key: _KT, /) -> _VT_co: ...
         def __reversed__(self) -> Iterator[_KT]: ...
         def __iter__(self) -> Iterator[_KT]: ...
         def __hash__(self) -> int: ...
         def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
-        def __or__(self, value: dict[_T1, _T2] | frozendict[_T1, _T2], /) -> frozendict[_KT | _T1, _VT | _T2]: ...
+        def __or__(self, value: dict[_T1, _T2] | frozendict[_T1, _T2], /) -> frozendict[_KT | _T1, _VT_co | _T2]: ...
 
         @overload
-        def __ror__(self, value: dict[_T1, _T2], /) -> dict[_KT | _T1, _VT | _T2]: ...
+        def __ror__(self, value: dict[_T1, _T2], /) -> dict[_KT | _T1, _VT_co | _T2]: ...
         @overload
-        def __ror__(self, value: frozendict[_T1, _T2], /) -> frozendict[_KT | _T1, _VT | _T2]: ...
+        def __ror__(self, value: frozendict[_T1, _T2], /) -> frozendict[_KT | _T1, _VT_co | _T2]: ...
 
 @disjoint_base
 class set(MutableSet[_T]):