diff --git a/telethon/extensions/messagepacker.py b/telethon/extensions/messagepacker.py
index fe7b1e6b..394cb4ae 100644
--- a/telethon/extensions/messagepacker.py
+++ b/telethon/extensions/messagepacker.py
@@ -53,8 +53,9 @@ class MessagePacker:
         batch = []
         size = 0
 
-        # Fill a new batch to return while the size is small enough
-        while self._deque:
+        # Fill a new batch to return while the size is small enough,
+        # as long as we don't exceed the maximum length of messages.
+        while self._deque and len(batch) <= MessageContainer.MAXIMUM_LENGTH:
             state = self._deque.popleft()
             size += len(state.data) + TLMessage.SIZE_OVERHEAD
 
diff --git a/telethon/tl/core/messagecontainer.py b/telethon/tl/core/messagecontainer.py
index 800a31f0..f93f7b53 100644
--- a/telethon/tl/core/messagecontainer.py
+++ b/telethon/tl/core/messagecontainer.py
@@ -15,6 +15,11 @@ class MessageContainer(TLObject):
     # The overhead of the container itself is subtracted.
     MAXIMUM_SIZE = 1044456 - 8
 
+    # Maximum amount of messages that can't be sent inside a single
+    # container, inclusive. Beyond this limit Telegram will respond
+    # with BAD_MESSAGE 64 (invalid container).
+    MAXIMUM_LENGTH = 1024
+
     def __init__(self, messages):
         self.messages = messages