diff --git a/paperqa/types.py b/paperqa/types.py
index 432a5326f..e1ab86f66 100644
--- a/paperqa/types.py
+++ b/paperqa/types.py
@@ -665,7 +665,7 @@ def source_quality_message(self) -> str:
     def is_hydration_needed(
         self,
         exclusion: Collection[str] = OPTIONAL_HYDRATION_FIELDS,
-        inclusion: Collection[str] = [],
+        inclusion: Collection[str] = (),
     ) -> bool:
         """Determine if we have unfilled attributes."""
         if inclusion: