diff --git a/changelog.d/6406.bugfix b/changelog.d/6406.bugfix
new file mode 100644
index 0000000000..ca9bee084b
--- /dev/null
+++ b/changelog.d/6406.bugfix
@@ -0,0 +1 @@
+Fix bug: TypeError in `register_user()` while using LDAP auth module.
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index f1b059986d..099611d79e 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -278,7 +278,7 @@ class RegistrationHandler(BaseHandler):
             }
 
             # Bind email to new account
-            yield self._register_email_threepid(user_id, threepid_dict, None, False)
+            yield self._register_email_threepid(user_id, threepid_dict, None)
 
         # Prevent the new user from showing up in the user directory if the server
         # mandates it.