diff --git a/src/Lean/Elab/Task.lean b/src/Lean/Elab/Task.lean
index 4248920ef2..aeebc74517 100644
--- a/src/Lean/Elab/Task.lean
+++ b/src/Lean/Elab/Task.lean
@@ -51,6 +51,11 @@ def asTask (t : CoreM α) : CoreM (BaseIO Unit × Task (CoreM α)) := do
   -- but modify it to return both the result and state
   let wrappedAct ← Core.wrapAsync (fun () => do let a ← t; let s ← get; return (a, s)) (some cancelToken)
   let task ← (wrappedAct ()).asTask
+  -- Propagate parent cancel token to child: when the parent is cancelled,
+  -- the child token is set too. This ensures that subtasks spawned via `asTask`
+  -- respond to server-level cancellation (e.g. on re-elaboration).
+  if let some parentTk := (← read).cancelTk? then
+    parentTk.onSet cancelToken.set
   return (cancelToken.set, task.map (sync := true) fun result =>
     match result with
     | .ok (a, s) => do
diff --git a/tests/server_interactive/cancellation_par.lean.out.expected b/tests/server_interactive/cancellation_par.lean.out.expected
index 2f11c7a36a..b16d7e5966 100644
--- a/tests/server_interactive/cancellation_par.lean.out.expected
+++ b/tests/server_interactive/cancellation_par.lean.out.expected
@@ -2,7 +2,5 @@ blocked!
 cancelled!
 blocked!
 cancelled!
-attempt_all_par: leaked!
 blocked!
 cancelled!
-first_par: leaked!