diff --git a/distributed/scheduler.py b/distributed/scheduler.py
index af28226388..fe8d1c61f8 100644
--- a/distributed/scheduler.py
+++ b/distributed/scheduler.py
@@ -708,6 +708,7 @@ def active(self):
 
     @property
     def active_states(self):
+        tg: TaskGroup
         return merge_with(sum, [tg._states for tg in self.active])
 
     def __repr__(self):