From 53a6264aa9d08d57bb6657b629d841ff18fa22cf Mon Sep 17 00:00:00 2001
From: Matthew Roeschke <emailformattr@gmail.com>
Date: Mon, 11 Feb 2019 10:53:42 -0800
Subject: [PATCH] BUG: DataFrame.join on tz-aware DatetimeIndex (#25260)

(cherry picked from commit a9a03a25d82ee285b6da48bfb20b9057d20bb9e7)
---
 doc/source/whatsnew/v0.24.2.rst         |  2 +-
 pandas/core/reshape/merge.py            |  2 +-
 pandas/tests/reshape/merge/test_join.py | 22 ++++++++++++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/doc/source/whatsnew/v0.24.2.rst b/doc/source/whatsnew/v0.24.2.rst
index 5ae777ca68ebac..f17c4974cd450c 100644
--- a/doc/source/whatsnew/v0.24.2.rst
+++ b/doc/source/whatsnew/v0.24.2.rst
@@ -79,7 +79,7 @@ Bug Fixes
 **Reshaping**
 
 -
--
+- Bug in :func:`DataFrame.join` when joining on a timezone aware :class:`DatetimeIndex` (:issue:`23931`)
 -
 
 **Visualization**
diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
index e11847d2b8ce26..adfd69c21d715a 100644
--- a/pandas/core/reshape/merge.py
+++ b/pandas/core/reshape/merge.py
@@ -862,7 +862,7 @@ def _get_merge_keys(self):
                               in zip(self.right.index.levels,
                                      self.right.index.codes)]
             else:
-                right_keys = [self.right.index.values]
+                right_keys = [self.right.index._values]
         elif _any(self.right_on):
             for k in self.right_on:
                 if is_rkey(k):
diff --git a/pandas/tests/reshape/merge/test_join.py b/pandas/tests/reshape/merge/test_join.py
index e21f9d0291afa8..c2a214446bb516 100644
--- a/pandas/tests/reshape/merge/test_join.py
+++ b/pandas/tests/reshape/merge/test_join.py
@@ -773,6 +773,28 @@ def test_join_multi_to_multi(self, join_type):
         with pytest.raises(ValueError, match=msg):
             right.join(left, on=['abc', 'xy'], how=join_type)
 
+    def test_join_on_tz_aware_datetimeindex(self):
+        # GH 23931
+        df1 = pd.DataFrame(
+            {
+                'date': pd.date_range(start='2018-01-01', periods=5,
+                                      tz='America/Chicago'),
+                'vals': list('abcde')
+            }
+        )
+
+        df2 = pd.DataFrame(
+            {
+                'date': pd.date_range(start='2018-01-03', periods=5,
+                                      tz='America/Chicago'),
+                'vals_2': list('tuvwx')
+            }
+        )
+        result = df1.join(df2.set_index('date'), on='date')
+        expected = df1.copy()
+        expected['vals_2'] = pd.Series([np.nan] * len(expected), dtype=object)
+        assert_frame_equal(result, expected)
+
 
 def _check_join(left, right, result, join_col, how='left',
                 lsuffix='_x', rsuffix='_y'):