diff --git a/tractor/_actor.py b/tractor/_actor.py
index 0614431..b73781c 100644
--- a/tractor/_actor.py
+++ b/tractor/_actor.py
@@ -537,11 +537,14 @@ class Actor:
                 async for msg in chan:
 
                     if msg is None:  # loop terminate sentinel
+
                         log.debug(
                             f"Cancelling all tasks for {chan} from {chan.uid}")
-                        for (channel, cid) in self._rpc_tasks:
+
+                        for (channel, cid) in self._rpc_tasks.copy():
                             if channel is chan:
                                 await self._cancel_task(cid, channel)
+
                         log.debug(
                                 f"Msg loop signalled to terminate for"
                                 f" {chan} from {chan.uid}")