1 files changed, 3 insertions, 0 deletions
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 68d143410f..00fa07c225 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -540,6 +540,9 @@ class ServerConfig(Config):
         if not isinstance(self.users_new_default_push_rules, list):
             raise ConfigError("'users_new_default_push_rules' must be a list")
 
+        # Turn the list into a set to improve lookup speed.
+        self.users_new_default_push_rules = set(self.users_new_default_push_rules)
+
     def has_tls_listener(self) -> bool:
         return any(listener.tls for listener in self.listeners)