diff --git a/libervia/backend/plugins/plugin_xep_0277.py b/libervia/backend/plugins/plugin_xep_0277.py
index b624f2e9..c489025e 100644
--- a/libervia/backend/plugins/plugin_xep_0277.py
+++ b/libervia/backend/plugins/plugin_xep_0277.py
@@ -782,7 +782,7 @@ class XEP_0277:
         host.bridge.add_method(
             "mb_preview",
             ".plugin",
-            in_sign="ssss",
+            in_sign="ss",
             out_sign="s",
             method=self._mb_preview,
             async_=True,