diff --git a/telethon/client/updates.py b/telethon/client/updates.py
index 854860fd..7019b465 100644
--- a/telethon/client/updates.py
+++ b/telethon/client/updates.py
@@ -1,4 +1,5 @@
 import asyncio
+import inspect
 import itertools
 import random
 import time
@@ -424,7 +425,9 @@ class UpdateMethods:
             if not builder.resolved:
                 await builder.resolve(self)
 
-            if not builder.filter(event):
+            filter = builder.filter(event)
+            filter = (await filter) if inspect.isawaitable(filter) else filter
+            if not filter:
                 continue
 
             try:
diff --git a/telethon/events/common.py b/telethon/events/common.py
index 42586608..fd3315f5 100644
--- a/telethon/events/common.py
+++ b/telethon/events/common.py
@@ -55,7 +55,7 @@ class EventBuilder(abc.ABC):
             which will be ignored if ``blacklist_chats=True``.
 
         func (`callable`, optional):
-            A callable function that should accept the event as input
+            A callable (async or not) function that should accept the event as input
             parameter, and return a value indicating whether the event
             should be dispatched or not (any truthy value will do, it
             does not need to be a `bool`). It works like a custom filter:
@@ -106,12 +106,13 @@ class EventBuilder(abc.ABC):
     def filter(self, event):
         """
         If the ID of ``event._chat_peer`` isn't in the chats set (or it is
-        but the set is a blacklist) returns `None`, otherwise the event.
+        but the set is a blacklist) returns `True`, otherwise `False`.
+        May also return awaitable which awaits to bool-able value.
 
         The events must have been resolved before this can be called.
         """
         if not self.resolved:
-            return None
+            return
 
         if self.chats is not None:
             # Note: the `event.chat_id` property checks if it's `None` for us
@@ -119,10 +120,12 @@ class EventBuilder(abc.ABC):
             if inside == self.blacklist_chats:
                 # If this chat matches but it's a blacklist ignore.
                 # If it doesn't match but it's a whitelist ignore.
-                return None
+                return
 
-        if not self.func or self.func(event):
-            return event
+        if not self.func:
+            return True
+
+        return self.func(event)
 
 
 class EventCommon(ChatGetter, abc.ABC):
diff --git a/telethon/tl/custom/conversation.py b/telethon/tl/custom/conversation.py
index c0d59e03..663acc08 100644
--- a/telethon/tl/custom/conversation.py
+++ b/telethon/tl/custom/conversation.py
@@ -1,5 +1,6 @@
 import asyncio
 import functools
+import inspect
 import itertools
 import time
 
@@ -312,9 +313,13 @@ class Conversation(ChatGetter):
         for key, (ev, fut) in list(self._custom.items()):
             ev_type = type(ev)
             inst = built[ev_type]
-            if inst and ev.filter(inst):
-                fut.set_result(inst)
-                del self._custom[key]
+
+            if inst:
+                filter = ev.filter(inst)
+                filter = (await filter) if inspect.isawaitable(filter) else filter
+                if filter:
+                    fut.set_result(inst)
+                    del self._custom[key]
 
     def _on_new_message(self, response):
         response = response.message