diff --git a/test/test_expose.py b/test/test_expose.py
index 48d59b28..5f3113ae 100644
--- a/test/test_expose.py
+++ b/test/test_expose.py
@@ -487,7 +487,7 @@ def validator(cls, value, ctx):
                     return None
 
                 if not isinstance(value['a'], str):
-                    return f'value for input `a` should be a str, but got: {type(value['a'])}'
+                    return f'value for input `a` should be a str, but got: {type(value["a"])}'
 
         class ExposeProcess(NewLoopProcess):
             @classmethod