diff --git a/mautrix_telegram/portal.py b/mautrix_telegram/portal.py
index 5644e06b..c3846ac2 100644
--- a/mautrix_telegram/portal.py
+++ b/mautrix_telegram/portal.py
@@ -584,10 +584,11 @@ class Portal:
 
     async def leave_matrix(self, user, source, event_id):
         if not user.logged_in:
-            response = await self.bot.client.send_message(
-                self.peer, f"__{user.displayname} left the room.__", markdown=True)
-            space = self.tgid if self.peer_type == "channel" else self.bot.tgid
-            self.is_duplicate(response, (event_id, space))
+            async with self.require_send_lock(self.bot.tgid):
+                response = await self.bot.client.send_message(
+                    self.peer, f"__{user.displayname} left the room.__", markdown=True)
+                space = self.tgid if self.peer_type == "channel" else self.bot.tgid
+                self.is_duplicate(response, (event_id, space))
             return
 
         if self.peer_type == "user":
@@ -615,10 +616,11 @@ class Portal:
 
     async def join_matrix(self, user, event_id):
         if not user.logged_in:
-            response = await self.bot.client.send_message(
-                self.peer, f"__{user.displayname} joined the room.__", markdown=True)
-            space = self.tgid if self.peer_type == "channel" else self.bot.tgid
-            self.is_duplicate(response, (event_id, space))
+            async with self.require_send_lock(self.bot.tgid):
+                response = await self.bot.client.send_message(
+                    self.peer, f"__{user.displayname} joined the room.__", markdown=True)
+                space = self.tgid if self.peer_type == "channel" else self.bot.tgid
+                self.is_duplicate(response, (event_id, space))
             return
 
         if self.peer_type == "channel":