diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 00000000..6f3bdf56
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,24 @@
+"""Pytest configuration for PyPortfolioOpt tests.
+
+Fixes compatibility between pytest-randomly and numpy's legacy
+random seed API. See https://github.com/PyPortfolio/PyPortfolioOpt/issues/725
+"""
+
+import numpy as np
+
+_original_np_random_seed = np.random.seed
+
+
+def _safe_np_random_seed(seed=None):
+      """Constrain seed to numpy's valid range [0, 2**32 - 1].
+
+          pytest-randomly may generate seeds exceeding this range when combining
+              the base seed with per-test offsets, causing ValueError in numpy's
+                  legacy random API.
+                      """
+      if seed is not None and isinstance(seed, (int, np.integer)):
+                seed = seed % (2**32)
+            _original_np_random_seed(seed)
+
+
+np.random.seed = _safe_np_random_seed
diff --git a/tests/test_conftest.py b/tests/test_conftest.py
new file mode 100644
index 00000000..ebabea23
--- /dev/null
+++ b/tests/test_conftest.py
@@ -0,0 +1,46 @@
+"""Tests for the conftest.py seed safety patch."""
+
+import numpy as np
+import pytest
+
+
+class TestSafeNumpySeed:
+      """Verify numpy.random.seed handles oversized seeds from pytest-randomly."""
+
+    def test_seed_exceeding_uint32_max(self):
+              """Seeds above 2**32 - 1 should not raise ValueError."""
+              np.random.seed(2**32 + 12345)
+
+    def test_seed_at_uint32_boundary(self):
+              """Seed exactly at 2**32 should wrap to 0."""
+              np.random.seed(2**32)
+
+    def test_seed_zero(self):
+              """Seed 0 should work as normal."""
+              np.random.seed(0)
+
+    def test_seed_max_valid(self):
+              """Seed 2**32 - 1 should work as normal."""
+              np.random.seed(2**32 - 1)
+
+    def test_seed_none(self):
+              """Seed None should work as normal (random seed)."""
+              np.random.seed(None)
+
+    def test_determinism_preserved(self):
+              """Patched seed should still produce deterministic results."""
+              np.random.seed(42)
+              a = np.random.rand(5)
+              np.random.seed(42)
+              b = np.random.rand(5)
+              np.testing.assert_array_equal(a, b)
+
+    def test_large_seed_determinism(self):
+              """Oversized seeds should produce deterministic results."""
+              large_seed = 2**33 + 99
+              np.random.seed(large_seed)
+              a = np.random.rand(5)
+              np.random.seed(large_seed)
+              b = np.random.rand(5)
+              np.testing.assert_array_equal(a, b)
+