diff --git a/saqc/core/translation/basescheme.py b/saqc/core/translation/basescheme.py
index 1a74597bd74d62ec075c5a24827d074a9c049411..712a0f03bd64078f76b997b5ab7c59db36a8dfb2 100644
--- a/saqc/core/translation/basescheme.py
+++ b/saqc/core/translation/basescheme.py
@@ -30,7 +30,7 @@ class TranslationScheme:  # pragma: no cover
         pass
 
     @abstractmethod
-    def __call__(self, ExternalFlag) -> float:
+    def __call__(self, flag: ExternalFlag) -> float:
         pass
 
     @abstractmethod