diff --git a/pandas/tests/window/test_online.py b/pandas/tests/window/test_online.py
index c7580650926da..461c62c07326d 100644
--- a/pandas/tests/window/test_online.py
+++ b/pandas/tests/window/test_online.py
@@ -22,6 +22,7 @@ def test_invalid_update(self):
         ):
             online_ewm.mean(update=df.head(1))
 
+    @pytest.mark.slow
     @pytest.mark.parametrize(
         "obj", [DataFrame({"a": range(5), "b": range(5)}), Series(range(5), name="foo")]
     )