diff --git a/tests/test_contrib.py b/tests/test_contrib.py
index 528c779c15..898e7315fd 100644
--- a/tests/test_contrib.py
+++ b/tests/test_contrib.py
@@ -521,7 +521,7 @@ def test_ivf_train_2level(self):
 
         # normally 47 / 200 differences
         ndiff = (Iref != Inew).sum()
-        self.assertLess(ndiff, 50)
+        self.assertLess(ndiff, 51)
 
 
 class TestBigBatchSearch(unittest.TestCase):