diff --git a/moto/ssm/exceptions.py b/moto/ssm/exceptions.py
index 14bb94c68..29813c22d 100644
--- a/moto/ssm/exceptions.py
+++ b/moto/ssm/exceptions.py
@@ -144,7 +144,7 @@ class ParameterMaxVersionLimitExceeded(JsonRESTError):
 class ParameterAlreadyExists(JsonRESTError):
     code = 400
 
-    def __init__(self):
+    def __init__(self) -> None:
         super().__init__(
             "ParameterAlreadyExists",
             "The parameter already exists. To overwrite this value, set the overwrite option in the request to true.",