diff --git a/pandas/tests/frame/methods/test_join.py b/pandas/tests/frame/methods/test_join.py
index 989a9be181a3f..b09ea596efe5b 100644
--- a/pandas/tests/frame/methods/test_join.py
+++ b/pandas/tests/frame/methods/test_join.py
@@ -373,3 +373,12 @@ def test_frame_join_tzaware(self):
 
         tm.assert_index_equal(result.index, expected)
         assert result.index.tz.zone == "US/Central"
+
+
+def test_join_duplicate_indicies():
+    # GH#43700 addresses issue GH#36336
+    df1 = pd.DataFrame(np.random.randn(5), index=[0, 1, 2, 3, 3], columns=["a"])
+    df2 = pd.DataFrame(np.random.randn(5), index=[0, 1, 2, 2, 4], columns=["b"])
+    result = df1.join(df2, how="outer")
+    expected = pd.concat([df1, df2], axis=1)
+    tm.assert_frame_equal(result, expected)