diff --git a/tests/federation/test_complexity.py b/tests/federation/test_complexity.py
index 3072fdaf9dbd..c499d9d9d6ea 100644
--- a/tests/federation/test_complexity.py
+++ b/tests/federation/test_complexity.py
@@ -13,8 +13,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from mock import Mock
+
 from twisted.internet import defer
 
+from synapse.api.errors import Codes, SynapseError
 from synapse.config.ratelimiting import FederationRateLimitConfig
 from synapse.federation.transport import server
 from synapse.rest import admin