diff --git a/reacton/utils.py b/reacton/utils.py
index f11c0d3..a66b6c4 100644
--- a/reacton/utils.py
+++ b/reacton/utils.py
@@ -19,7 +19,7 @@ def without_default(func: Callable, kwargs):
     return non_default_kwargs
 
 
-def implements(f: Callable[P, T]):
+def implements(f: Callable[P, T]) -> Callable[[Callable], Callable[P, T]]:
     def caster(fimpl: Callable) -> Callable[P, T]:
         # wraps gives us the right signature at runtime (such as Jupyter)
         return cast(Callable[P, T], functools.wraps(f)(fimpl))
diff --git a/reacton/utils_test.py b/reacton/utils_test.py
index 646d0dd..d3bfd74 100644
--- a/reacton/utils_test.py
+++ b/reacton/utils_test.py
@@ -118,7 +118,7 @@ def make_el(a):
         def on_click():
             pass
 
-        return w.Button(on_click=on_click, label=f"{a}")
+        return w.Button(on_click=on_click, description=f"{a}")
 
     el1 = make_el(1)
     el2 = make_el(1)