diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 72792a25cf55ac..416c346be2ecd1 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -35,7 +35,9 @@ def all_tasks(loop=None):
     """Return a set of all tasks for the loop."""
     if loop is None:
         loop = events.get_running_loop()
-    return {t for t in _all_tasks
+    # NB: set(_all_tasks) is required to protect
+    # from https://bugs.python.org/issue34970 bug
+    return {t for t in list(_all_tasks)
             if futures._get_loop(t) is loop and not t.done()}
 
 
@@ -45,7 +47,9 @@ def _all_tasks_compat(loop=None):
     # method.
     if loop is None:
         loop = events.get_event_loop()
-    return {t for t in _all_tasks if futures._get_loop(t) is loop}
+    # NB: set(_all_tasks) is required to protect
+    # from https://bugs.python.org/issue34970 bug
+    return {t for t in list(_all_tasks) if futures._get_loop(t) is loop}
 
 
 class Task(futures._PyFuture):  # Inherit Python Task implementation
diff --git a/Misc/NEWS.d/next/Library/2018-10-13-11-14-13.bpo-34970.SrJTY7.rst b/Misc/NEWS.d/next/Library/2018-10-13-11-14-13.bpo-34970.SrJTY7.rst
new file mode 100644
index 00000000000000..a58b3dd354194a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-10-13-11-14-13.bpo-34970.SrJTY7.rst
@@ -0,0 +1 @@
+Protect tasks weak set manipulation in ``asyncio.all_tasks()``