diff --git a/xarray/core/merge.py b/xarray/core/merge.py
index 38b95bc0379..2aa086d73d6 100644
--- a/xarray/core/merge.py
+++ b/xarray/core/merge.py
@@ -2,7 +2,7 @@
 
 from collections import defaultdict
 from collections.abc import Hashable, Iterable, Mapping, Sequence, Set
-from typing import TYPE_CHECKING, Any, NamedTuple
+from typing import TYPE_CHECKING, Any, NamedTuple, Union
 
 import pandas as pd
 
@@ -24,18 +24,18 @@
     from xarray.core.dataset import Dataset
     from xarray.core.types import CombineAttrsOptions, CompatOptions, JoinOptions
 
-    DimsLike = Hashable | Sequence[Hashable]
+    DimsLike = Union[Hashable, Sequence[Hashable]]  # noqa
     ArrayLike = Any
-    VariableLike = (
-        ArrayLike
-        | tuple[DimsLike, ArrayLike]
-        | tuple[DimsLike, ArrayLike, Mapping]
-        | tuple[DimsLike, ArrayLike, Mapping, Mapping]
-    )
-    XarrayValue = DataArray | Variable | VariableLike
-    DatasetLike = Dataset | Coordinates | Mapping[Any, XarrayValue]
-    CoercibleValue = XarrayValue | pd.Series | pd.DataFrame
-    CoercibleMapping = Dataset | Mapping[Any, CoercibleValue]
+    VariableLike = Union[  # noqa
+        ArrayLike,
+        tuple[DimsLike, ArrayLike],
+        tuple[DimsLike, ArrayLike, Mapping],
+        tuple[DimsLike, ArrayLike, Mapping, Mapping],
+    ]
+    XarrayValue = Union[DataArray, Variable, VariableLike]  # noqa
+    DatasetLike = Union[Dataset, Coordinates, Mapping[Any, XarrayValue]]  # noqa
+    CoercibleValue = Union[XarrayValue, pd.Series, pd.DataFrame]  # noqa
+    CoercibleMapping = Union[Dataset, Mapping[Any, CoercibleValue]]  # noqa
 
 
 PANDAS_TYPES = (pd.Series, pd.DataFrame)