diff --git a/src/lib/python/isc/memmgr/builder.py b/src/lib/python/isc/memmgr/builder.py
index f01f830c75..2e8b71ca5c 100644
--- a/src/lib/python/isc/memmgr/builder.py
+++ b/src/lib/python/isc/memmgr/builder.py
@@ -91,7 +91,7 @@ class MemorySegmentBuilder:
                         # notified. Instead return this in the response
                         # queue.
                         with self._lock:
-                            self._response_queue.append('bad_command')
+                            self._response_queue.append(('bad_command',))
                             # In this case, we do not notify the main
                             # thread about a response on the socket, as
                             # we quit the main loop here anyway (and any
diff --git a/src/lib/python/isc/memmgr/tests/builder_tests.py b/src/lib/python/isc/memmgr/tests/builder_tests.py
index 2b21337284..230f39618d 100644
--- a/src/lib/python/isc/memmgr/tests/builder_tests.py
+++ b/src/lib/python/isc/memmgr/tests/builder_tests.py
@@ -73,7 +73,10 @@ class TestMemorySegmentBuilder(unittest.TestCase):
         with self._builder_lock:
             self.assertEqual(len(self._builder_command_queue), 0)
             self.assertEqual(len(self._builder_response_queue), 1)
-            self.assertListEqual(self._builder_response_queue, ['bad_command'])
+
+            response = self._builder_response_queue[0]
+            self.assertTrue(isinstance(response, tuple))
+            self.assertTupleEqual(response, ('bad_command',))
             self._builder_response_queue.clear()
 
     def test_shutdown(self):