diff --git a/pandas/tests/series/indexing/test_datetime.py b/pandas/tests/series/indexing/test_datetime.py
index 61a9909926efe..e2f40c6267493 100644
--- a/pandas/tests/series/indexing/test_datetime.py
+++ b/pandas/tests/series/indexing/test_datetime.py
@@ -604,28 +604,24 @@ def test_indexing_over_size_cutoff():
         _index._SIZE_CUTOFF = old_cutoff
 
 
-def test_indexing_over_size_cutoff_period_index():
+def test_indexing_over_size_cutoff_period_index(monkeypatch):
     # GH 27136
 
-    old_cutoff = _index._SIZE_CUTOFF
-    try:
-        _index._SIZE_CUTOFF = 1000
+    monkeypatch.setattr(_index, "_SIZE_CUTOFF", 1000)
 
-        n = 1100
-        idx = pd.period_range("1/1/2000", freq="T", periods=n)
-        assert idx._engine.over_size_threshold
+    n = 1100
+    idx = pd.period_range("1/1/2000", freq="T", periods=n)
+    assert idx._engine.over_size_threshold
 
-        s = pd.Series(np.random.randn(len(idx)), index=idx)
+    s = pd.Series(np.random.randn(len(idx)), index=idx)
 
-        pos = n - 1
-        timestamp = idx[pos]
-        assert timestamp in s.index
+    pos = n - 1
+    timestamp = idx[pos]
+    assert timestamp in s.index
 
-        # it works!
-        s[timestamp]
-        assert len(s.loc[[timestamp]]) > 0
-    finally:
-        _index._SIZE_CUTOFF = old_cutoff
+    # it works!
+    s[timestamp]
+    assert len(s.loc[[timestamp]]) > 0
 
 
 def test_indexing_unordered():