diff --git a/test/test_utils.py b/test/test_utils.py
index 7a12ad27..493b9e7d 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -82,7 +82,8 @@ class ArrayContainerWithOptional:
     @dataclass
     class ArrayContainerWithInitFalse:
         x: np.ndarray
-        y: np.ndarray = field(default=np.zeros(42), init=False, repr=False)
+        y: np.ndarray = field(default_factory=lambda: np.zeros(42),
+                              init=False, repr=False)
 
     with pytest.raises(ValueError):
         # NOTE: init=False fields are not allowed