diff --git a/chatlab/registry.py b/chatlab/registry.py
index b79f09b..d461a7d 100644
--- a/chatlab/registry.py
+++ b/chatlab/registry.py
@@ -141,7 +141,7 @@ def extract_model_from_function(func_name: str, function: Callable) -> Type[Base
             raise Exception(f"`{name}` parameter of {func_name} must have a JSON-serializable type annotation")
         type_annotation = param.annotation
 
-        default_value = ...
+        default_value: Any = ...
 
         # determine if there is a default value
         if param.default != inspect.Parameter.empty: