diff --git a/synapse/config/server.py b/synapse/config/server.py
index f370b22c3..7840dc3ad 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -27,7 +27,7 @@ class ServerConfig(Config):
         self.daemonize = config.get("daemonize")
         self.print_pidfile = config.get("print_pidfile")
         self.user_agent_suffix = config.get("user_agent_suffix")
-        self.use_frozen_dicts = config.get("use_frozen_dicts", True)
+        self.use_frozen_dicts = config.get("use_frozen_dicts", False)
         self.public_baseurl = config.get("public_baseurl")
         self.secondary_directory_servers = config.get("secondary_directory_servers", [])
 
diff --git a/tests/utils.py b/tests/utils.py
index e19ae581e..6e41ae1ff 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -54,6 +54,7 @@ def setup_test_homeserver(name="test", datastore=None, config=None, **kargs):
         config.trusted_third_party_id_servers = []
         config.room_invite_state_types = []
 
+    config.use_frozen_dicts = True
     config.database_config = {"name": "sqlite3"}
 
     if "clock" not in kargs: