diff --git a/conservancy_beancount/plugin/core.py b/conservancy_beancount/plugin/core.py
index 62df122..c9c8af1 100644
--- a/conservancy_beancount/plugin/core.py
+++ b/conservancy_beancount/plugin/core.py
@@ -69,12 +69,10 @@ class Hook(Generic[Entry], metaclass=abc.ABCMeta):
     @abc.abstractmethod
     def run(self, entry: Entry) -> errormod.Iter: ...
 
-    def __init_subclass__(cls) -> None:
-        # cls.__orig_bases__ comes from the ABCMeta metaclass
-        cls.DIRECTIVE = cls.__orig_bases__[0].__args__[0]  # type:ignore[attr-defined]
 
+class TransactionHook(Hook[Transaction]):
+    DIRECTIVE = Transaction
 
-TransactionHook = Hook[Transaction]
 
 ### HELPER CLASSES