diff --git a/.github/workflows/python-dev.yml b/.github/workflows/python-dev.yml
index 220c1e464742e..9076b66683a29 100644
--- a/.github/workflows/python-dev.yml
+++ b/.github/workflows/python-dev.yml
@@ -73,7 +73,7 @@ jobs:
       run: |
         python --version
         python -m pip install --upgrade pip setuptools wheel
-        python -m pip install -i https://pypi.anaconda.org/scipy-wheels-nightly/simple numpy
+        python -m pip install --extra-index-url https://pypi.anaconda.org/scipy-wheels-nightly/simple numpy
         python -m pip install git+https://github.com/nedbat/coveragepy.git
         python -m pip install versioneer[toml]
         python -m pip install python-dateutil pytz cython hypothesis==6.52.1 pytest>=6.2.5 pytest-xdist pytest-cov pytest-asyncio>=0.17
diff --git a/pandas/tests/frame/test_unary.py b/pandas/tests/frame/test_unary.py
index a69ca0fef7f8b..9caadd0998a26 100644
--- a/pandas/tests/frame/test_unary.py
+++ b/pandas/tests/frame/test_unary.py
@@ -3,6 +3,8 @@
 import numpy as np
 import pytest
 
+from pandas.compat import is_numpy_dev
+
 import pandas as pd
 import pandas._testing as tm
 
@@ -98,11 +100,6 @@ def test_pos_numeric(self, df):
     @pytest.mark.parametrize(
         "df",
         [
-            # numpy changing behavior in the future
-            pytest.param(
-                pd.DataFrame({"a": ["a", "b"]}),
-                marks=[pytest.mark.filterwarnings("ignore")],
-            ),
             pd.DataFrame({"a": np.array([-1, 2], dtype=object)}),
             pd.DataFrame({"a": [Decimal("-1.0"), Decimal("2.0")]}),
         ],
@@ -112,6 +109,25 @@ def test_pos_object(self, df):
         tm.assert_frame_equal(+df, df)
         tm.assert_series_equal(+df["a"], df["a"])
 
+    @pytest.mark.parametrize(
+        "df",
+        [
+            pytest.param(
+                pd.DataFrame({"a": ["a", "b"]}),
+                marks=[pytest.mark.filterwarnings("ignore")],
+            ),
+        ],
+    )
+    def test_pos_object_raises(self, df):
+        # GH#21380
+        if is_numpy_dev:
+            with pytest.raises(
+                TypeError, match=r"^bad operand type for unary \+: \'str\'$"
+            ):
+                tm.assert_frame_equal(+df, df)
+        else:
+            tm.assert_series_equal(+df["a"], df["a"])
+
     @pytest.mark.parametrize(
         "df", [pd.DataFrame({"a": pd.to_datetime(["2017-01-22", "1970-01-01"])})]
     )