diff -r a14b93a4eb49 Lib/asyncio/tasks.py
--- a/Lib/asyncio/tasks.py	Mon Jun 20 05:29:54 2016 +0300
+++ b/Lib/asyncio/tasks.py	Mon Jun 20 12:48:50 2016 +0200
@@ -579,9 +579,10 @@
     def cancel(self):
         if self.done():
             return False
+        ret = False
         for child in self._children:
-            child.cancel()
-        return True
+            ret |= child.cancel()
+        return ret
 
 
 def gather(*coros_or_futures, loop=None, return_exceptions=False):
diff -r a14b93a4eb49 Lib/test/test_asyncio/test_tasks.py
--- a/Lib/test/test_asyncio/test_tasks.py	Mon Jun 20 05:29:54 2016 +0300
+++ b/Lib/test/test_asyncio/test_tasks.py	Mon Jun 20 12:48:50 2016 +0200
@@ -1857,6 +1857,36 @@
     def test_cancel_wait_for(self):
         self._test_cancel_wait_for(60.0)
 
+    def test_cancel_gather(self):
+        """Ensure that a gathering future refuses to be cancelled once all
+        children are done"""
+        loop = asyncio.new_event_loop()
+        self.addCleanup(loop.close)
+
+        fut = asyncio.Future(loop=loop)
+        # The indirection fut->child_coro is needed since otherwise the
+        # gathering task is done at the same time as the child future
+        def child_coro():
+            return (yield from fut)
+        gather_future = asyncio.gather(child_coro(), loop=loop)
+        gather_task = asyncio.ensure_future(gather_future, loop=loop)
+
+        cancel_result = None
+        def cancelling_callback(_):
+            nonlocal cancel_result
+            cancel_result = gather_task.cancel()
+        fut.add_done_callback(cancelling_callback)
+
+        fut.set_result(42) # calls the cancelling_callback after fut is done()
+
+        # At this point the task should complete.
+        loop.run_until_complete(gather_task)
+
+        # Python issue #26923: asyncio.gather drops cancellation
+        self.assertEqual(cancel_result, False)
+        self.assertFalse(gather_task.cancelled())
+        self.assertEqual(gather_task.result(), [42])
+
 
 class GatherTestsBase: