diff --git a/src/semra/client.py b/src/semra/client.py
index 73aace4..badfde0 100644
--- a/src/semra/client.py
+++ b/src/semra/client.py
@@ -28,7 +28,7 @@
 
 TxResult: TypeAlias = t.Optional[list[list[Any]]]
 
-ReferenceHint: TypeAlias = str | Reference
+ReferenceHint: TypeAlias = t.Union[str, Reference]
 
 
 class Neo4jClient: