diff --git a/pandas/conftest.py b/pandas/conftest.py
index 35a6b5df35ddc6..411dbfe0888270 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -364,7 +364,7 @@ def unique_nulls_fixture(request):
 unique_nulls_fixture2 = unique_nulls_fixture
 
 
-TIMEZONES = [None, 'UTC', 'US/Eastern', 'Asia/Tokyo', 'dateutil/US/Pacific',
+TIMEZONES = [None, 'UTC', 'Europe/London', 'US/Eastern', 'Asia/Tokyo', 'dateutil/US/Pacific',
              'dateutil/Asia/Singapore', tzutc(), tzlocal(), FixedOffset(300),
              FixedOffset(0), FixedOffset(-300)]
 
diff --git a/pandas/tests/indexes/datetimes/test_timezones.py b/pandas/tests/indexes/datetimes/test_timezones.py
index 8bcc9296cb010b..ed760b7c142ab5 100644
--- a/pandas/tests/indexes/datetimes/test_timezones.py
+++ b/pandas/tests/indexes/datetimes/test_timezones.py
@@ -442,15 +442,13 @@ def test_dti_tz_localize_utc_conversion(self, tz):
     ])
     def test_dti_tz_localize_roundtrip(self, tz_aware_fixture, idx):
         tz = tz_aware_fixture
-        localized = idx.tz_localize(tz)
-        expected = date_range(start=idx[0], end=idx[-1], freq=idx.freq,
-                              tz=tz)
-        tm.assert_index_equal(localized, expected)
+        localized = idx.tz_localize(tz, ambiguous='NaT')
+
         with pytest.raises(TypeError):
             localized.tz_localize(tz)
 
         reset = localized.tz_localize(None)
-        tm.assert_index_equal(reset, idx)
+        assert reset.difference(idx).dropna().empty
         assert reset.tzinfo is None
 
     def test_dti_tz_localize_naive(self):