diff --git a/pyproject.toml b/pyproject.toml
index 4cccbdc..49c273d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -92,7 +92,7 @@ select = [
     "D300",
     "D417",
     "D419",
-
+    "NPY201",
 ]
 
 ignore = [
diff --git a/tests/nested_pandas/nestedframe/test_nestedframe.py b/tests/nested_pandas/nestedframe/test_nestedframe.py
index fffbbe9..7590fce 100644
--- a/tests/nested_pandas/nestedframe/test_nestedframe.py
+++ b/tests/nested_pandas/nestedframe/test_nestedframe.py
@@ -174,10 +174,10 @@ def test_query():
 def test_dropna():
     """Test that dropna works on all layers"""
 
-    base = NestedFrame(data={"a": [1, 2, 3], "b": [2, np.NaN, 6]}, index=[0, 1, 2])
+    base = NestedFrame(data={"a": [1, 2, 3], "b": [2, np.nan, 6]}, index=[0, 1, 2])
 
     nested = pd.DataFrame(
-        data={"c": [0, 2, 4, 1, np.NaN, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
+        data={"c": [0, 2, 4, 1, np.nan, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
         index=[0, 0, 0, 1, 1, 1, 2, 2, 2],
     )
 
@@ -216,10 +216,10 @@ def test_dropna_layer_as_base_column():
 def test_dropna_inplace_base():
     """Test in-place behavior of dropna"""
 
-    base = NestedFrame(data={"a": [1, 2, 3], "b": [np.NaN, 4, 6]}, index=[0, 1, 2])
+    base = NestedFrame(data={"a": [1, 2, 3], "b": [np.nan, 4, 6]}, index=[0, 1, 2])
 
     nested = pd.DataFrame(
-        data={"c": [0, 2, 4, 1, np.NaN, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
+        data={"c": [0, 2, 4, 1, np.nan, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
         index=[0, 0, 0, 1, 1, 1, 2, 2, 2],
     )
 
@@ -237,10 +237,10 @@ def test_dropna_inplace_base():
 def test_dropna_inplace_nested():
     """Test in-place behavior of dropna"""
 
-    base = NestedFrame(data={"a": [1, 2, 3], "b": [np.NaN, 4, 6]}, index=[0, 1, 2])
+    base = NestedFrame(data={"a": [1, 2, 3], "b": [np.nan, 4, 6]}, index=[0, 1, 2])
 
     nested = pd.DataFrame(
-        data={"c": [0, 2, 4, 1, np.NaN, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
+        data={"c": [0, 2, 4, 1, np.nan, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
         index=[0, 0, 0, 1, 1, 1, 2, 2, 2],
     )
 
@@ -258,10 +258,10 @@ def test_dropna_inplace_nested():
 def test_dropna_errors():
     """Test that the various dropna exceptions trigger"""
 
-    base = NestedFrame(data={"a": [1, 2, 3], "b": [2, np.NaN, 6]}, index=[0, 1, 2])
+    base = NestedFrame(data={"a": [1, 2, 3], "b": [2, np.nan, 6]}, index=[0, 1, 2])
 
     nested = pd.DataFrame(
-        data={"c": [0, 2, 4, 1, np.NaN, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
+        data={"c": [0, 2, 4, 1, np.nan, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
         index=[0, 0, 0, 1, 1, 1, 2, 2, 2],
     )
 
diff --git a/tests/nested_pandas/series/test_accessor.py b/tests/nested_pandas/series/test_accessor.py
index a9c5549..a4ac4db 100644
--- a/tests/nested_pandas/series/test_accessor.py
+++ b/tests/nested_pandas/series/test_accessor.py
@@ -805,7 +805,7 @@ def test_to_flat_dropna():
     """
 
     flat = pd.DataFrame(
-        data={"c": [0, 2, 4, 1, np.NaN, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
+        data={"c": [0, 2, 4, 1, np.nan, 3, 1, 4, 1], "d": [5, 4, 7, 5, 3, 1, 9, 3, 4]},
         index=[0, 0, 0, 1, 1, 1, 2, 2, 2],
     )
     nested = pack_flat(flat, name="nested")
diff --git a/tests/nested_pandas/utils/test_utils.py b/tests/nested_pandas/utils/test_utils.py
index 43e4648..e1403a8 100644
--- a/tests/nested_pandas/utils/test_utils.py
+++ b/tests/nested_pandas/utils/test_utils.py
@@ -10,10 +10,10 @@ def test_count_nested(join):
     """Test the functionality of count nested"""
 
     # Initialize test data
-    base = NestedFrame(data={"a": [1, 2, 3], "b": [2, np.NaN, 6]}, index=[0, 1, 2])
+    base = NestedFrame(data={"a": [1, 2, 3], "b": [2, np.nan, 6]}, index=[0, 1, 2])
     nested = pd.DataFrame(
         data={
-            "c": [0, 2, 4, 1, np.NaN, 3, 1, 4, 1],
+            "c": [0, 2, 4, 1, np.nan, 3, 1, 4, 1],
             "d": [5, 4, 7, 5, 3, 1, 9, 3, 4],
             "label": ["a", "a", "b", "b", "a", "a", "b", "a", "b"],
         },