diff --git a/telethon/client/updates.py b/telethon/client/updates.py
index 0dff677a..57cd4962 100644
--- a/telethon/client/updates.py
+++ b/telethon/client/updates.py
@@ -89,7 +89,7 @@ class UpdateMethods(UserMethods):
         elif not event:
             event = events.Raw()
 
-        self._loop.create_task(event.resolve(self))
+        event.ensure_resolve(self)
         self._event_builders.append((event, callback))
 
     def remove_event_handler(self, callback, event=None):
@@ -266,10 +266,8 @@ class UpdateMethods(UserMethods):
             if not event:
                 continue
 
-            # TODO Lock until it's resolved; the task for resolving
-            # was already created when adding the event handler.
-            if not builder.resolved:
-                await builder.resolve()
+            if not builder.resolved.is_set():
+                await builder.resolved.wait()
 
             if not builder.filter(event):
                 continue
diff --git a/telethon/events/common.py b/telethon/events/common.py
index e1eb2ee6..7c706e66 100644
--- a/telethon/events/common.py
+++ b/telethon/events/common.py
@@ -1,4 +1,5 @@
 import abc
+import asyncio
 import warnings
 
 from .. import utils
@@ -57,26 +58,48 @@ class EventBuilder(abc.ABC):
     def __init__(self, chats=None, blacklist_chats=False):
         self.chats = chats
         self.blacklist_chats = blacklist_chats
-        self.resolved = False
+        self.resolved = None
 
     @classmethod
     @abc.abstractmethod
     def build(cls, update):
         """Builds an event for the given update if possible, or returns None"""
 
+    def ensure_resolve(self, client):
+        """
+        Sets the event loop so that self.resolved can be used.
+
+        The expected workflow is:
+        1. Creating the event builder.
+        2a. Calling `ensure_resolve`.
+        2b. Awaiting `resolved.wait`.
+        OR
+        2a. Awaiting `resolve`.
+        3. Using `filter`.
+        """
+        if not self.resolved:
+            self.resolved = asyncio.Event(loop=client.loop)
+            client.loop.create_task(self.resolve(client))
+
     async def resolve(self, client):
         """Helper method to allow event builders to be resolved before usage"""
-        if not self.resolved:
-            self.resolved = True
+        if not self.resolved.is_set():
             self.chats = await _into_id_set(client, self.chats)
             if not EventBuilder.self_id:
                 EventBuilder.self_id = await client.get_peer_id('me')
 
+            self.resolved.set()
+
     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.
+
+        The events must have been resolved before this can be called.
         """
+        if not self.resolved:
+            return None
+
         if self.chats is not None:
             inside = utils.get_peer_id(event._chat_peer) in self.chats
             if inside == self.blacklist_chats:
diff --git a/telethon/events/newmessage.py b/telethon/events/newmessage.py
index 902a6f73..b2ee33e1 100644
--- a/telethon/events/newmessage.py
+++ b/telethon/events/newmessage.py
@@ -1,7 +1,8 @@
+import asyncio
 import re
 
 from .common import EventBuilder, EventCommon, name_inner_event, _into_id_set
-from ..tl import types, custom
+from ..tl import types
 
 
 @name_inner_event
@@ -71,9 +72,9 @@ class NewMessage(EventBuilder):
         ))
 
     async def resolve(self, client):
-        if not self.resolved:
-            await super().resolve(client)
+        if not self.resolved.is_set():
             self.from_users = await _into_id_set(client, self.from_users)
+            await super().resolve(client)
 
     @classmethod
     def build(cls, update):
diff --git a/telethon/tl/custom/conversation.py b/telethon/tl/custom/conversation.py
index bc32633a..c6c00bf9 100644
--- a/telethon/tl/custom/conversation.py
+++ b/telethon/tl/custom/conversation.py
@@ -260,6 +260,9 @@ class Conversation(ChatGetter):
         if isinstance(event, type):
             event = event()
 
+        # Since we await resolve here we don't need to await resolved.
+        # We know it has already been resolved, unlike when normally
+        # adding an event handler, for which a task is created to resolve.
         await event.resolve()
 
         counter = Conversation._custom_counter
@@ -276,9 +279,6 @@ class Conversation(ChatGetter):
         return await result()
 
     async def _check_custom(self, built):
-        # TODO This code is quite much a copy paste of registering events
-        # in the client, resolving them and setting the client; perhaps
-        # there is a better way?
         for i, (ev, fut) in self._custom.items():
             ev_type = type(ev)
             if built[ev_type] and ev.filter(built[ev_type]):