diff --git a/libs/lib/xaal/lib/core.py b/libs/lib/xaal/lib/core.py
index 716ecda6cc3c74d8b6b2519309890f313a25a5d5..e85a03ec95996eb9440317e7e5c0c2d887a8f322 100644
--- a/libs/lib/xaal/lib/core.py
+++ b/libs/lib/xaal/lib/core.py
@@ -37,8 +37,8 @@ FuncT = TypeVar("FuncT", Callable[[], None], Callable[[], Awaitable[None]])
 # Function type w/ message as argument (subscribers), no return
 SubFuncT = TypeVar(
         "SubFuncT",
-        Callable[[str], None],
-        Callable[[str], Awaitable[None]]
+        Callable[['Message'], None],
+        Callable[['Message'], Awaitable[None]]
 )
 
 logger = logging.getLogger(__name__)