diff --git a/changelog.d/6406.bugfix b/changelog.d/6406.bugfix
new file mode 100644
index 000000000..ca9bee084
--- /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 95806af41..8a7d965fe 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -266,7 +266,7 @@ 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)
 
         return user_id