diff --git a/src/functions_framework/_typed_event.py b/src/functions_framework/_typed_event.py
index 40e715a..05e3602 100644
--- a/src/functions_framework/_typed_event.py
+++ b/src/functions_framework/_typed_event.py
@@ -31,7 +31,7 @@
 
 def register_typed_event(decorator_type, func):
     try:
-        sig = signature(func)
+        sig = signature(func, eval_str=True)
         annotation_type = list(sig.parameters.values())[0].annotation
         input_type = _select_input_type(decorator_type, annotation_type)
         _validate_input_type(input_type)