diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 07aec6a0d833f..1380c5caed1c9 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -2302,27 +2302,15 @@ def union(self, other):
                                            allow_fill=False)
                 result = _concat._concat_compat((lvals, other_diff))
 
-                try:
-                    lvals[0] < other_diff[0]
-                except TypeError as e:
-                    warnings.warn("%s, sort order is undefined for "
-                                  "incomparable objects" % e, RuntimeWarning,
-                                  stacklevel=3)
-                else:
-                    types = frozenset((self.inferred_type,
-                                       other.inferred_type))
-                    if not types & _unsortable_types:
-                        result.sort()
-
             else:
                 result = lvals
 
-                try:
-                    result = np.sort(result)
-                except TypeError as e:
-                    warnings.warn("%s, sort order is undefined for "
-                                  "incomparable objects" % e, RuntimeWarning,
-                                  stacklevel=3)
+            try:
+                result = sorting.safe_sort(result)
+            except TypeError as e:
+                warnings.warn("%s, sort order is undefined for "
+                              "incomparable objects" % e, RuntimeWarning,
+                              stacklevel=3)
 
         # for subclasses
         return self._wrap_setop_result(other, result)
diff --git a/pandas/tests/indexes/test_base.py b/pandas/tests/indexes/test_base.py
index b13110a04e1c1..2108206a8cbe5 100644
--- a/pandas/tests/indexes/test_base.py
+++ b/pandas/tests/indexes/test_base.py
@@ -805,8 +805,7 @@ def test_union_name_preservation(self, first_list, second_list, first_name,
 
     def test_union_dt_as_obj(self):
         # TODO: Replace with fixturesult
-        with tm.assert_produces_warning(RuntimeWarning):
-            firstCat = self.strIndex.union(self.dateIndex)
+        firstCat = self.strIndex.union(self.dateIndex)
         secondCat = self.strIndex.union(self.strIndex)
 
         if self.dateIndex.dtype == np.object_:
@@ -1615,7 +1614,7 @@ def test_drop_tuple(self, values, to_drop):
     @pytest.mark.parametrize("method,expected", [
         ('intersection', np.array([(1, 'A'), (2, 'A'), (1, 'B'), (2, 'B')],
                                   dtype=[('num', int), ('let', 'a1')])),
-        ('union', np.array([(1, 'A'), (2, 'A'), (1, 'B'), (2, 'B'), (1, 'C'),
+        ('union', np.array([(1, 'A'), (1, 'B'), (1, 'C'), (2, 'A'), (2, 'B'),
                             (2, 'C')], dtype=[('num', int), ('let', 'a1')]))
     ])
     def test_tuple_union_bug(self, method, expected):
@@ -2242,10 +2241,7 @@ def test_copy_name(self):
         s1 = Series(2, index=first)
         s2 = Series(3, index=second[:-1])
 
-        warning_type = RuntimeWarning if PY3 else None
-        with tm.assert_produces_warning(warning_type):
-            # Python 3: Unorderable types
-            s3 = s1 * s2
+        s3 = s1 * s2
 
         assert s3.index.name == 'mario'
 
@@ -2274,16 +2270,9 @@ def test_union_base(self):
         first = index[3:]
         second = index[:5]
 
-        if PY3:
-            # unorderable types
-            warn_type = RuntimeWarning
-        else:
-            warn_type = None
-
-        with tm.assert_produces_warning(warn_type):
-            result = first.union(second)
+        result = first.union(second)
 
-        expected = Index(['b', 2, 'c', 0, 'a', 1])
+        expected = Index([0, 1, 2, 'a', 'b', 'c'])
         tm.assert_index_equal(result, expected)
 
     @pytest.mark.parametrize("klass", [
@@ -2294,14 +2283,7 @@ def test_union_different_type_base(self, klass):
         first = index[3:]
         second = index[:5]
 
-        if PY3:
-            # unorderable types
-            warn_type = RuntimeWarning
-        else:
-            warn_type = None
-
-        with tm.assert_produces_warning(warn_type):
-            result = first.union(klass(second.values))
+        result = first.union(klass(second.values))
 
         assert tm.equalContents(result, index)
 
diff --git a/pandas/tests/series/test_operators.py b/pandas/tests/series/test_operators.py
index f6fb5f0c46cc8..4d3c9926fc5ae 100644
--- a/pandas/tests/series/test_operators.py
+++ b/pandas/tests/series/test_operators.py
@@ -120,24 +120,12 @@ def test_operators_bitwise(self):
             s_0123 & [0.1, 4, 3.14, 2]
 
         # s_0123 will be all false now because of reindexing like s_tft
-        if compat.PY3:
-            # unable to sort incompatible object via .union.
-            exp = Series([False] * 7, index=['b', 'c', 'a', 0, 1, 2, 3])
-            with tm.assert_produces_warning(RuntimeWarning):
-                assert_series_equal(s_tft & s_0123, exp)
-        else:
-            exp = Series([False] * 7, index=[0, 1, 2, 3, 'a', 'b', 'c'])
-            assert_series_equal(s_tft & s_0123, exp)
+        exp = Series([False] * 7, index=[0, 1, 2, 3, 'a', 'b', 'c'])
+        assert_series_equal(s_tft & s_0123, exp)
 
         # s_tft will be all false now because of reindexing like s_0123
-        if compat.PY3:
-            # unable to sort incompatible object via .union.
-            exp = Series([False] * 7, index=[0, 1, 2, 3, 'b', 'c', 'a'])
-            with tm.assert_produces_warning(RuntimeWarning):
-                assert_series_equal(s_0123 & s_tft, exp)
-        else:
-            exp = Series([False] * 7, index=[0, 1, 2, 3, 'a', 'b', 'c'])
-            assert_series_equal(s_0123 & s_tft, exp)
+        exp = Series([False] * 7, index=[0, 1, 2, 3, 'a', 'b', 'c'])
+        assert_series_equal(s_0123 & s_tft, exp)
 
         assert_series_equal(s_0123 & False, Series([False] * 4))
         assert_series_equal(s_0123 ^ False, Series([False, True, True, True]))
@@ -280,11 +268,7 @@ def test_logical_ops_label_based(self):
             assert_series_equal(result, a[a])
 
         for e in [Series(['z'])]:
-            if compat.PY3:
-                with tm.assert_produces_warning(RuntimeWarning):
-                    result = a[a | e]
-            else:
-                result = a[a | e]
+            result = a[a | e]
             assert_series_equal(result, a[a])
 
         # vs scalars