2 files changed, 2 insertions, 2 deletions
diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py
index 60ecc498ab..d55b93d763 100644
--- a/synapse/util/__init__.py
+++ b/synapse/util/__init__.py
@@ -45,7 +45,7 @@ def unwrapFirstError(failure):
     return failure.value.subFailure
 
 
-@attr.s
+@attr.s(slots=True)
 class Clock:
     """
     A Clock wraps a Twisted reactor and provides utilities on top of it.
diff --git a/synapse/util/caches/__init__.py b/synapse/util/caches/__init__.py
index 237f588658..8fc05be278 100644
--- a/synapse/util/caches/__init__.py
+++ b/synapse/util/caches/__init__.py
@@ -42,7 +42,7 @@ response_cache_evicted = Gauge(
 response_cache_total = Gauge("synapse_util_caches_response_cache:total", "", ["name"])
 
 
-@attr.s
+@attr.s(slots=True)
 class CacheMetric:
 
     _cache = attr.ib()