diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index dd84c5f5e9ba..ee3a2269a847 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -54,7 +54,7 @@ def check_username(self, localpart, guest_access_token=None,
                 Codes.INVALID_USERNAME
             )
 
-        if len(localpart) == 0:
+        if not localpart:
             raise SynapseError(
                 400,
                 "User ID cannot be empty",