diff --git a/numpyro/primitives.py b/numpyro/primitives.py
index 0359aaa64..d227a0943 100644
--- a/numpyro/primitives.py
+++ b/numpyro/primitives.py
@@ -4,7 +4,7 @@
 from collections import namedtuple
 from contextlib import ExitStack, contextmanager
 import functools
-from typing import Callable, Generator, Optional, cast
+from typing import Callable, Generator, Optional, Union, cast
 import warnings
 
 import jax
@@ -235,7 +235,7 @@ def sample(
 
 
 def param(
-    name: str, init_value: Optional[ArrayLike | Callable] = None, **kwargs
+    name: str, init_value: Optional[Union[ArrayLike, Callable]] = None, **kwargs
 ) -> Array:
     """
     Annotate the given site as an optimizable parameter for use with
@@ -319,7 +319,9 @@ def deterministic(name: str, value: ArrayLike) -> Array:
     return msg["value"]
 
 
-def mutable(name: str, init_value: Optional[ArrayLike] = None) -> ArrayLike | None:
+def mutable(
+    name: str, init_value: Optional[ArrayLike] = None
+) -> Union[ArrayLike, None]:
     """
     This primitive is used to store a mutable value that can be changed
     during model execution::
@@ -375,7 +377,7 @@ def _inspect() -> dict:
     return msg
 
 
-def get_mask() -> ArrayLike | None:
+def get_mask() -> Union[ArrayLike, None]:
     """
     Records the effects of enclosing ``handlers.mask`` handlers.
     This is useful for avoiding expensive ``numpyro.factor()`` computations during
@@ -641,7 +643,7 @@ def factor(name: str, log_factor: ArrayLike) -> None:
     sample(name, unit_dist, obs=unit_value, infer={"is_auxiliary": True})
 
 
-def prng_key() -> Array | None:
+def prng_key() -> Union[Array, None]:
     """
     A statement to draw a pseudo-random number generator key
     :func:`~jax.random.PRNGKey` under :class:`~numpyro.handlers.seed` handler.