diff --git a/_delb/names.py b/_delb/names.py
index b8750899..64850fa7 100644
--- a/_delb/names.py
+++ b/_delb/names.py
@@ -127,7 +127,7 @@ def __len__(self) -> int:
     def __str__(self) -> str:
         return str(self.__data)
 
-    def lookup_prefix(self, namespace: str) -> Optional[str]:
+    def lookup_prefix(self, namespace: str) -> str | None:
         """
         Resolves a namespace to a prefix while considering namespace declarations of
         ascending nodes.