diff --git a/telethon/utils.py b/telethon/utils.py
index 917eb85b..d94734a2 100644
--- a/telethon/utils.py
+++ b/telethon/utils.py
@@ -52,9 +52,7 @@ def get_extension(media):
 def get_input_peer(entity):
     """Gets the input peer for the given "entity" (user, chat or channel).
        A ValueError is raised if the given entity isn't a supported type."""
-    if any(isinstance(entity, c) for c in (
-        InputPeerUser, InputPeerChat, InputPeerChannel,
-            InputPeerSelf, InputPeerEmpty)):
+    if type(entity).subclass_of_id == 0xc91c90b6:  # crc32('InputUser')
         return entity
 
     if isinstance(entity, User):
diff --git a/telethon_generator/tl_generator.py b/telethon_generator/tl_generator.py
index 042c29dc..8ccc4d65 100755
--- a/telethon_generator/tl_generator.py
+++ b/telethon_generator/tl_generator.py
@@ -2,6 +2,7 @@
 import os
 import re
 import shutil
+from zlib import crc32
 from collections import defaultdict
 
 try:
@@ -214,6 +215,9 @@ class TLGenerator:
         # Class-level variable to store its constructor ID
         builder.writeln("# Telegram's constructor (U)ID for this class")
         builder.writeln('constructor_id = {}'.format(hex(tlobject.id)))
+        builder.writeln("# Also the ID of its resulting type for fast checks")
+        builder.writeln('subclass_of_id = {}'.format(
+            hex(crc32(tlobject.result.encode('ascii')))))
         builder.writeln()
 
         # Flag arguments must go last