diff --git a/moto/utilities/id_generator.py b/moto/utilities/id_generator.py
index 53abaa8787c2..22aa58c90d22 100644
--- a/moto/utilities/id_generator.py
+++ b/moto/utilities/id_generator.py
@@ -47,7 +47,7 @@ def unique_identifier(self) -> str:
             [self.account_id, self.region, self.service, self.resource, self.name]
         )
 
-    def __str__(self):
+    def __str__(self) -> str:
         return self.unique_identifier