diff --git a/tiled/structures/core.py b/tiled/structures/core.py
index 853afcead..2e9d0b73c 100644
--- a/tiled/structures/core.py
+++ b/tiled/structures/core.py
@@ -36,7 +36,7 @@ def __repr__(self):
             output = f"{type(self).__name__}({self.name!r}, version={self.version!r})"
         return output
 
-    def dict(self) -> dict[str, str | None]:
+    def dict(self) -> dict[str, Optional[str]]:
         # For easy interoperability with pydantic 1.x models
         return asdict(self)