diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 6a0aaea92c..e015680d0a 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -48,4 +48,4 @@ class RegistrationConfig(Config):
             args.disable_registration = True
 
         if args.registration_shared_secret is None:
-            args.registration_shared_secret= random_string_with_symbols(50)
+            args.registration_shared_secret = random_string_with_symbols(50)