diff --git a/copulas/multivariate/tree.py b/copulas/multivariate/tree.py
index 70ee7d4e..8cbcfb1e 100644
--- a/copulas/multivariate/tree.py
+++ b/copulas/multivariate/tree.py
@@ -98,7 +98,7 @@ def _sort_tau_by_y(self, y):
         """
         # first column is the variable of interest
         tau_y = self.tau_matrix[:, y]
-        tau_y[y] = np.NaN
+        tau_y[y] = np.nan
 
         temp = np.empty([self.n_nodes, 3])
         temp[:, 0] = np.arange(self.n_nodes)
diff --git a/pyproject.toml b/pyproject.toml
index 5070f2c9..d22c242e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -21,9 +21,9 @@ license = { text = 'BSL-1.1' }
 requires-python = '>=3.8,<3.13'
 readme = 'README.md'
 dependencies = [
-    "numpy>=1.21.0,<2.0.0;python_version<'3.10'",
-    "numpy>=1.23.3,<2.0.0;python_version>='3.10' and python_version<'3.12'",
-    "numpy>=1.26.0,<2.0.0;python_version>='3.12'",
+    "numpy>=1.21.0;python_version<'3.10'",
+    "numpy>=1.23.3;python_version>='3.10' and python_version<'3.12'",
+    "numpy>=1.26.0;python_version>='3.12'",
     "pandas>=1.4.0;python_version<'3.11'",
     "pandas>=1.5.0;python_version>='3.11' and python_version<'3.12'",
     "pandas>=2.1.1;python_version>='3.12'",