diff --git a/sat/plugins/plugin_misc_text_commands.py b/sat/plugins/plugin_misc_text_commands.py
index 51fe728f..5f9e42a6 100644
--- a/sat/plugins/plugin_misc_text_commands.py
+++ b/sat/plugins/plugin_misc_text_commands.py
@@ -327,7 +327,7 @@ class TextCommands(object):
             if arg[-1] != "@":
                 return jid.JID(arg)
             return jid.JID(arg + service_jid)
-        return jid.JID("%s@%s" % (arg, service_jid))
+        return jid.JID(f"{arg}@{service_jid}")
 
     def feedBack(self, client, message, mess_data, info_type=FEEDBACK_INFO_TYPE):
         """Give a message back to the user"""
diff --git a/sat/plugins/plugin_xep_0045.py b/sat/plugins/plugin_xep_0045.py
index 2e99a01f..a06d7742 100644
--- a/sat/plugins/plugin_xep_0045.py
+++ b/sat/plugins/plugin_xep_0045.py
@@ -674,10 +674,19 @@ class XEP_0045(object):
         @command (all): JID
             - JID: room to join (on the same service if full jid is not specified)
         """
-        if mess_data["unparsed"].strip():
-            room_jid = self.text_cmds.getRoomJID(mess_data["unparsed"].strip(), mess_data["to"].host)
-            nick = (self.getRoomNick(client, room_jid) or
-                    client.jid.user)
+        room_raw = mess_data["unparsed"].strip()
+        if room_raw:
+            if self.isJoinedRoom(client, mess_data["to"]):
+                # we use the same service as the one from the room where the command has
+                # been entered if full jid is not entered
+                muc_service = mess_data["to"].host
+                nick = self.getRoomNick(client, mess_data["to"]) or client.jid.user
+            else:
+                # the command has been entered in a one2one conversation, so we use
+                # our server MUC service as default service
+                muc_service = client.muc_service or ""
+                nick = client.jid.user
+            room_jid = self.text_cmds.getRoomJID(room_raw, muc_service)
             self.join(client, room_jid, nick, {})
 
         return False
@@ -688,8 +697,9 @@ class XEP_0045(object):
         @command (group): [ROOM_JID]
             - ROOM_JID: jid of the room to live (current room if not specified)
         """
-        if mess_data["unparsed"].strip():
-            room = self.text_cmds.getRoomJID(mess_data["unparsed"].strip(), mess_data["to"].host)
+        room_raw = mess_data["unparsed"].strip()
+        if room_raw:
+            room = self.text_cmds.getRoomJID(room_raw, mess_data["to"].host)
         else:
             room = mess_data["to"]