diff --git a/changelog.d/6406.bugfix b/changelog.d/6406.bugfix
new file mode 100644
index 0000000000000000000000000000000000000000..ca9bee084bb5fcc8abddf44ba1357bae5319f9c1
--- /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 95806af41e4fd6a6f732768e562b9165b430ee1f..8a7d965feb02142da4002337839476b69a11dbc8 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