diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index c4d025b465df..5d50dd9e3dfc 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -152,6 +152,7 @@ def on_POST(self, request):
 
         desired_username = params.get("username", None)
         new_password = params.get("password", None)
+        guest_access_token = params.get("guest_access_token", None)
 
         (user_id, token) = yield self.registration_handler.register(
             localpart=desired_username,