diff --git a/mastodon/Mastodon.py b/mastodon/Mastodon.py
index 9a77749..48e0e7a 100644
--- a/mastodon/Mastodon.py
+++ b/mastodon/Mastodon.py
@@ -223,6 +223,8 @@ class Mastodon:
                 raise MastodonIllegalArgumentError('Invalid user name, password, or redirect_uris: %s' % e)
             elif code is not None:
                 raise MastodonIllegalArgumentError('Invalid access token or redirect_uris: %s' % e)
+            else:
+                raise MastodonIllegalArgumentError('Invalid request: %s' % e)
 
         requested_scopes = " ".join(sorted(scopes))
         received_scopes = " ".join(sorted(response["scope"].split(" ")))