diff --git a/sat/core/xmpp.py b/sat/core/xmpp.py
index 5580eaf0..26ce0935 100644
--- a/sat/core/xmpp.py
+++ b/sat/core/xmpp.py
@@ -1010,6 +1010,10 @@ class SatMessageProtocol(xmppim.MessageProtocol):
         xmppim.MessageProtocol.__init__(self)
         self.host = host
 
+    @property
+    def client(self):
+        return self.parent
+
     def parseMessage(self, message_elt):
         """Parse a message XML and return message_data
 
@@ -1141,6 +1145,7 @@ class SatMessageProtocol(xmppim.MessageProtocol):
                 media_type = mimetypes.guess_type(attachment['name'], strict=False)[0]
                 if media_type:
                     attachment[C.MESS_KEY_ATTACHMENTS_MEDIA_TYPE] = media_type
+
         return data
 
     def skipEmptyMessage(self, data):
@@ -1431,6 +1436,9 @@ class SatRosterProtocol(xmppim.RosterClientProtocol):
 
     def isJidInRoster(self, entity_jid):
         """Return True if jid is in roster"""
+        if not isinstance(entity_jid, jid.JID):
+            raise exceptions.InternalError(
+                f"a JID is expected, not {type(entity_jid)}: {entity_jid!r}")
         return entity_jid in self._jids
 
     def isPresenceAuthorised(self, entity_jid):