diff --git a/telethon/events/common.py b/telethon/events/common.py
index 45032207..8cecb2a6 100644
--- a/telethon/events/common.py
+++ b/telethon/events/common.py
@@ -69,7 +69,7 @@ class EventBuilder(abc.ABC):
 
     def __init__(self, chats=None, *, blacklist_chats=False, func=None):
         self.chats = chats
-        self.blacklist_chats = blacklist_chats
+        self.blacklist_chats = bool(blacklist_chats)
         self.resolved = False
         self.func = func
         self._resolve_lock = None
diff --git a/telethon/events/messageread.py b/telethon/events/messageread.py
index 48f478be..fd8d73db 100644
--- a/telethon/events/messageread.py
+++ b/telethon/events/messageread.py
@@ -15,7 +15,7 @@ class MessageRead(EventBuilder):
             when messages you sent are read by someone else will fire it.
     """
     def __init__(
-            self, chats=None, *, blacklist_chats=None, func=None, inbox=False):
+            self, chats=None, *, blacklist_chats=False, func=None, inbox=False):
         super().__init__(chats, blacklist_chats=blacklist_chats, func=func)
         self.inbox = inbox