diff --git a/telethon/client/dialogs.py b/telethon/client/dialogs.py
index 67cd52d0..1191a724 100644
--- a/telethon/client/dialogs.py
+++ b/telethon/client/dialogs.py
@@ -160,7 +160,7 @@ class DialogMethods(UserMethods):
     def conversation(
             self, entity,
             *, timeout=None, total_timeout=60, max_messages=100,
-            replies_are_responses=True):
+            exclusive=True, replies_are_responses=True):
         """
         Creates a `Conversation <telethon.tl.custom.conversation.Conversation>`
         with the given entity so you can easily send messages and await for
@@ -187,6 +187,16 @@ class DialogMethods(UserMethods):
                 specified chat, subsequent actions will result in
                 ``ValueError``.
 
+            exclusive (`bool`, optional):
+                By default, conversations are exclusive within a single
+                chat. That means that while a conversation is open in a
+                chat, you can't open another one in the same chat, unless
+                you disable this flag.
+
+                If you try opening an exclusive conversation for
+                a chat where it's already open, it will raise
+                ``AlreadyInConversationError``.
+
             replies_are_responses (`bool`, optional):
                 Whether replies should be treated as responses or not.
 
@@ -229,6 +239,7 @@ class DialogMethods(UserMethods):
             timeout=timeout,
             total_timeout=total_timeout,
             max_messages=max_messages,
+            exclusive=exclusive,
             replies_are_responses=replies_are_responses
 
         )
diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index 60f6269f..90f42cf1 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -272,6 +272,7 @@ class TelegramBaseClient(abc.ABC):
         # Some further state for subclasses
         self._event_builders = []
         self._conversations = {}
+        self._ids_in_conversations = {}  # chat_id: count
 
         # Default parse mode
         self._parse_mode = markdown
diff --git a/telethon/client/updates.py b/telethon/client/updates.py
index 1c212d21..84c07eb4 100644
--- a/telethon/client/updates.py
+++ b/telethon/client/updates.py
@@ -283,6 +283,10 @@ class UpdateMethods(UserMethods):
 
             try:
                 await callback(event)
+            except errors.AlreadyInConversationError:
+                name = getattr(callback, '__name__', repr(callback))
+                __log__.debug('Event handler "%s" already has an open '
+                              'conversation, ignoring new one', name)
             except events.StopPropagation:
                 name = getattr(callback, '__name__', repr(callback))
                 __log__.debug(
diff --git a/telethon/errors/__init__.py b/telethon/errors/__init__.py
index 03125dc5..faf88e8d 100644
--- a/telethon/errors/__init__.py
+++ b/telethon/errors/__init__.py
@@ -8,7 +8,8 @@ from threading import Thread
 
 from .common import (
     ReadCancelledError, TypeNotFoundError, InvalidChecksumError,
-    InvalidBufferError, SecurityError, CdnFileTamperedError, MultiError
+    InvalidBufferError, SecurityError, CdnFileTamperedError,
+    AlreadyInConversationError, MultiError
 )
 
 # This imports the base errors too, as they're imported there
diff --git a/telethon/errors/common.py b/telethon/errors/common.py
index 65cd363c..c9f22b41 100644
--- a/telethon/errors/common.py
+++ b/telethon/errors/common.py
@@ -79,6 +79,17 @@ class CdnFileTamperedError(SecurityError):
         )
 
 
+class AlreadyInConversationError(Exception):
+    """
+    Occurs when another exclusive conversation is opened in the same chat.
+    """
+    def __init__(self):
+        super().__init__(
+            'Cannot open exclusive conversation in a '
+            'chat that already has one open conversation'
+        )
+
+
 class MultiError(Exception):
     """Exception container for multiple `TLRequest`'s."""
 
diff --git a/telethon/tl/custom/conversation.py b/telethon/tl/custom/conversation.py
index 66ec79f8..97b6816a 100644
--- a/telethon/tl/custom/conversation.py
+++ b/telethon/tl/custom/conversation.py
@@ -3,7 +3,7 @@ import itertools
 import time
 
 from .chatgetter import ChatGetter
-from ... import utils
+from ... import utils, errors
 
 
 class Conversation(ChatGetter):
@@ -23,7 +23,7 @@ class Conversation(ChatGetter):
 
     def __init__(self, client, input_chat,
                  *, timeout, total_timeout, max_messages,
-                 replies_are_responses):
+                 exclusive, replies_are_responses):
         self._id = Conversation._id_counter
         Conversation._id_counter += 1
 
@@ -50,6 +50,8 @@ class Conversation(ChatGetter):
         self._pending_edits = {}
         self._pending_reads = {}
 
+        self._exclusive = exclusive
+
         # The user is able to expect two responses for the same message.
         # {desired message ID: next incoming index}
         self._response_indices = {}
@@ -380,11 +382,20 @@ class Conversation(ChatGetter):
         return self._client.loop.run_until_complete(self.__aenter__())
 
     async def __aenter__(self):
-        self._client._conversations[self._id] = self
         self._input_chat = \
             await self._client.get_input_entity(self._input_chat)
 
         self._chat_peer = utils.get_peer(self._input_chat)
+
+        # Make sure we're the only conversation in this chat if it's exclusive
+        chat_id = utils.get_peer_id(self._chat_peer)
+        count = self._client._ids_in_conversations.get(chat_id, 0)
+        if self._exclusive and count:
+            raise errors.AlreadyInConversationError()
+
+        self._client._ids_in_conversations[chat_id] = count + 1
+        self._client._conversations[self._id] = self
+
         self._last_outgoing = 0
         self._last_incoming = 0
         for d in (
@@ -405,5 +416,11 @@ class Conversation(ChatGetter):
         return self._client.loop.run_until_complete(self.__aexit__(*args))
 
     async def __aexit__(self, *args):
+        chat_id = utils.get_peer_id(self._chat_peer)
+        if self._client._ids_in_conversations[chat_id] == 1:
+            del self._client._ids_in_conversations[chat_id]
+        else:
+            self._client._ids_in_conversations[chat_id] -= 1
+
         del self._client._conversations[self._id]
         self._cancel_all()