diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index 667656cb4de02..58c5e5155e4e8 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -2840,3 +2840,14 @@ def test_groupby_index_name_in_index_content(val_in, index, val_out):
     result = series.to_frame().groupby("blah").sum()
     expected = expected.to_frame()
     tm.assert_frame_equal(result, expected)
+
+
+def test_groupby_on_column_drops_na():
+    # GH 21755
+    df = DataFrame(
+        {"a": [np.nan, "foo", "bar", np.nan, np.nan, "baz"], "b": [0, 1, 2, 3, 4, 5]}
+    )
+    result = df.groupby("a").head(1)
+    expected = DataFrame({"a": ["foo", "bar", "baz"], "b": [1, 2, 5]}, index=[1, 2, 5])
+
+    tm.assert_frame_equal(result, expected)