diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index 4ca8b0e317bd2..2d5e03df78d2f 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -3245,3 +3245,12 @@ def test_get_group_axis_1():
         }
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_groupby_ffill_with_duplicated_index():
+    # GH#43412
+    df = DataFrame({"a": [1, 2, 3, 4, np.nan, np.nan]}, index=[0, 1, 2, 0, 1, 2])
+
+    result = df.groupby(level=0).ffill()
+    expected = DataFrame({"a": [1, 2, 3, 4, 2, 3]}, index=[0, 1, 2, 0, 1, 2])
+    tm.assert_frame_equal(result, expected, check_dtype=False)