2 files changed, 4 insertions, 1 deletions
diff --git a/synapse/logging/_terse_json.py b/synapse/logging/_terse_json.py
index 03934956f4..c0b9384189 100644
--- a/synapse/logging/_terse_json.py
+++ b/synapse/logging/_terse_json.py
@@ -171,7 +171,7 @@ class LogProducer(object):
 
     def stopProducing(self):
         self._paused = True
-        self._buffer = None
+        self._buffer = deque()
 
     def resumeProducing(self):
         self._paused = False
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index 6747f29e6a..33b322209d 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -405,6 +405,9 @@ class LoggingContext(object):
         """
         current = get_thread_resource_usage()
 
+        # Indicate to mypy that we know that self.usage_start is None.
+        assert self.usage_start is not None
+
         utime_delta = current.ru_utime - self.usage_start.ru_utime
         stime_delta = current.ru_stime - self.usage_start.ru_stime