diff --git a/test/contrib/hsgp/test_approximation.py b/test/contrib/hsgp/test_approximation.py
index 424a423ee..825659756 100644
--- a/test/contrib/hsgp/test_approximation.py
+++ b/test/contrib/hsgp/test_approximation.py
@@ -144,7 +144,7 @@ def test_kernel_approx_squared_exponential(
     def _exact_rbf(length):
         return RBF(length)(x1, x2).squeeze(axis=-1)
 
-    if isinstance(length, Union[float, int]):
+    if isinstance(length,  int) | isinstance(length, float):
         exact = _exact_rbf(length)
     elif length.ndim == 1:
         exact = _exact_rbf(length)