diff --git a/libervia/backend/plugins/plugin_xep_0277.py b/libervia/backend/plugins/plugin_xep_0277.py
index a72a0de6..f554ca59 100644
--- a/libervia/backend/plugins/plugin_xep_0277.py
+++ b/libervia/backend/plugins/plugin_xep_0277.py
@@ -139,6 +139,8 @@ class MbExtra(BaseModel):
     encrypted: bool = False
     encrypted_for: dict | None = None
     signed: bool = False
+    # FIXME: Must be moved to XEP-0372 plugin.
+    mentions: list[JIDType] = Field(default_factory=list)
 
 
 class MbData(BaseModel):