diff --git a/promise/async_.py b/promise/async_.py
index 5bb6bef..27d0977 100644
--- a/promise/async_.py
+++ b/promise/async_.py
@@ -108,11 +108,11 @@ def wait(self, promise, timeout=None):
         self.schedule.wait(target, timeout)
 
     def drain_queues(self):
-        assert self.is_tick_used
-        self.drain_queue(self.normal_queue)
-        self.reset()
-        self.have_drained_queues = True
-        self.drain_queue(self.late_queue)
+        if not self.is_tick_used:
+            self.drain_queue(self.normal_queue)
+            self.reset()
+            self.have_drained_queues = True
+            self.drain_queue(self.late_queue)
 
     def queue_tick(self):
         if not self.is_tick_used: