diff --git a/Lib/test/test_types.py b/Lib/test/test_types.py
index d940f1aaaf3..2d0e33f03c3 100644
--- a/Lib/test/test_types.py
+++ b/Lib/test/test_types.py
@@ -18,6 +18,11 @@ class Example:
 
 class Forward: ...
 
+def clear_typing_caches():
+    for f in typing._cleanups:
+        f()
+
+
 class TypesTests(unittest.TestCase):
 
     def test_truth_values(self):
@@ -710,11 +715,34 @@ class TypesTests(unittest.TestCase):
         self.assertIs((TV | int)[int], int)
 
     def test_union_args(self):
-        self.assertEqual((int | str).__args__, (int, str))
-        self.assertEqual(((int | str) | list).__args__, (int, str, list))
-        self.assertEqual((int | (str | list)).__args__, (int, str, list))
-        self.assertEqual((int | None).__args__, (int, type(None)))
-        self.assertEqual((int | type(None)).__args__, (int, type(None)))
+        def check(arg, expected):
+            clear_typing_caches()
+            self.assertEqual(arg.__args__, expected)
+
+        check(int | str, (int, str))
+        check((int | str) | list, (int, str, list))
+        check(int | (str | list), (int, str, list))
+        check((int | str) | int, (int, str))
+        check(int | (str | int), (int, str))
+        check((int | str) | (str | int), (int, str))
+        check(typing.Union[int, str] | list, (int, str, list))
+        check(int | typing.Union[str, list], (int, str, list))
+        check((int | str) | (list | int), (int, str, list))
+        check((int | str) | typing.Union[list, int], (int, str, list))
+        check(typing.Union[int, str] | (list | int), (int, str, list))
+        check((str | int) | (int | list), (str, int, list))
+        check((str | int) | typing.Union[int, list], (str, int, list))
+        check(typing.Union[str, int] | (int | list), (str, int, list))
+        check(int | type(None), (int, type(None)))
+        check(type(None) | int, (type(None), int))
+
+        args = (int, list[int], typing.List[int],
+                typing.Tuple[int, int], typing.Callable[[int], int],
+                typing.Hashable, typing.TypeVar('T'))
+        for x in args:
+            with self.subTest(x):
+                check(x | None, (x, type(None)))
+                check(None | x, (type(None), x))
 
     def test_union_parameter_chaining(self):
         T = typing.TypeVar("T")
diff --git a/Lib/typing.py b/Lib/typing.py
index ca05fb54bf4..2f2286813a4 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -988,8 +988,8 @@ class _GenericAlias(_BaseGenericAlias, _root=True):
     def __or__(self, right):
         return Union[self, right]
 
-    def __ror__(self, right):
-        return Union[self, right]
+    def __ror__(self, left):
+        return Union[left, self]
 
     @_tp_cache
     def __getitem__(self, params):
@@ -1099,8 +1099,8 @@ class _SpecialGenericAlias(_BaseGenericAlias, _root=True):
     def __or__(self, right):
         return Union[self, right]
 
-    def __ror__(self, right):
-        return Union[self, right]
+    def __ror__(self, left):
+        return Union[left, self]
 
 class _CallableGenericAlias(_GenericAlias, _root=True):
     def __repr__(self):
diff --git a/Objects/unionobject.c b/Objects/unionobject.c
index dad26c32b29..b3a65068626 100644
--- a/Objects/unionobject.c
+++ b/Objects/unionobject.c
@@ -260,8 +260,8 @@ dedup_and_flatten_args(PyObject* args)
     for (Py_ssize_t i = 0; i < arg_length; i++) {
         int is_duplicate = 0;
         PyObject* i_element = PyTuple_GET_ITEM(args, i);
-        for (Py_ssize_t j = i + 1; j < arg_length; j++) {
-            PyObject* j_element = PyTuple_GET_ITEM(args, j);
+        for (Py_ssize_t j = 0; j < added_items; j++) {
+            PyObject* j_element = PyTuple_GET_ITEM(new_args, j);
             int is_ga = PyObject_TypeCheck(i_element, &Py_GenericAliasType) &&
                         PyObject_TypeCheck(j_element, &Py_GenericAliasType);
             // RichCompare to also deduplicate GenericAlias types (slower)