diff --git a/RELEASE_NOTES.rst b/RELEASE_NOTES.rst
index 59846a38f..a3beab361 100644
--- a/RELEASE_NOTES.rst
+++ b/RELEASE_NOTES.rst
@@ -13,12 +13,16 @@ ARTIQ-5
   :class:`~artiq.coredevice.ad9914.AD9914` phase reference timestamp parameters
   have been renamed to ``ref_time_mu`` for consistency, as they are in machine
   units.
-* :func:`~artiq.tools.verbosity_args` renamed to :func:`~artiq.tools.add_common_args`. New feature: adds an option to print the ARTIQ version.
+* :func:`~artiq.tools.verbosity_args` has been renamed to
+  :func:`~artiq.tools.add_common_args`, and now adds a ``--version`` flag.
 * A gateware-level input edge counter has been added, which offers higher
   throughput and increased flexibility over the usual TTL input PHYs where
   edge timestamps are not required. See :mod:`artiq.coredevice.edge_counter` for
   the core device driver and :mod:`artiq.gateware.rtio.phy.edge_counter`/
   :meth:`artiq.gateware.eem.DIO.add_std` for the gateware components.
+* The controller manager now ignores device database entries without the
+  ``"command"`` key set to facilitate sharing of devices between multiple
+  masters.
 
 
 ARTIQ-4
diff --git a/artiq/test/test_ctlmgr.py b/artiq/test/test_ctlmgr.py
index 825fad38c..cfadbd4f7 100644
--- a/artiq/test/test_ctlmgr.py
+++ b/artiq/test/test_ctlmgr.py
@@ -6,6 +6,7 @@ import asyncio
 
 from artiq.devices.ctlmgr import Controllers
 from artiq.protocols.pc_rpc import AsyncioClient
+from artiq.tools import expect_no_log_messages
 
 logger = logging.getLogger(__name__)
 
@@ -70,3 +71,13 @@ class ControllerCase(unittest.TestCase):
             await remote.ping()
 
         self.loop.run_until_complete(test())
+
+    def test_no_command_controller(self):
+        entry = {
+            "type": "controller",
+            "host": "::1",
+            "port": 3253
+        }
+        with expect_no_log_messages(logging.ERROR):
+            self.controllers["lda_sim"] = entry
+            self.assertTrue(self.controllers.queue.empty())
diff --git a/artiq/tools.py b/artiq/tools.py
index e5517bebe..30941e7a6 100644
--- a/artiq/tools.py
+++ b/artiq/tools.py
@@ -1,6 +1,7 @@
 import asyncio
 import atexit
 import collections
+import contextlib
 import importlib.machinery
 import logging
 import os
@@ -16,6 +17,7 @@ from artiq.protocols import pyon
 
 __all__ = ["parse_arguments", "elide", "short_format", "file_import",
            "get_experiment", "add_common_args", "simple_network_args",
+           "UnexpectedLogMessageError", "expect_no_log_messages",
            "multiline_log_config", "init_logger", "bind_address_from_args",
            "atexit_register_coroutine", "exc_to_warning",
            "asyncio_wait_or_cancel", "TaskObject", "Condition",
@@ -142,6 +144,36 @@ def simple_network_args(parser, default_port):
                                help=h)
 
 
+class UnexpectedLogMessageError(Exception):
+    pass
+
+
+class FailingLogHandler(logging.Handler):
+    def emit(self, record):
+        raise UnexpectedLogMessageError("Unexpected log message: '{}'".format(
+            record.getMessage()))
+
+
+@contextlib.contextmanager
+def expect_no_log_messages(level, logger=None):
+    """Raise an UnexpectedLogMessageError if a log message of the given level
+    (or above) is emitted while the context is active.
+
+    Example: ::
+
+        with expect_no_log_messages(logging.ERROR):
+            do_stuff_that_should_not_log_errors()
+    """
+    if logger is None:
+        logger = logging.getLogger()
+    handler = FailingLogHandler(level)
+    logger.addHandler(handler)
+    try:
+        yield
+    finally:
+        logger.removeHandler(handler)
+
+
 class MultilineFormatter(logging.Formatter):
     def __init__(self):
         logging.Formatter.__init__(