diff --git a/generator/src/telethon_generator/_impl/codegen/generator.py b/generator/src/telethon_generator/_impl/codegen/generator.py
index d5cf8a01..713318a9 100644
--- a/generator/src/telethon_generator/_impl/codegen/generator.py
+++ b/generator/src/telethon_generator/_impl/codegen/generator.py
@@ -194,14 +194,14 @@ def generate(fs: FakeFs, tl: ParsedTl) -> None:
     writer.write(
         "from .core import Serializable, Reader, deserialize_bool, deserialize_i32_list, deserialize_i64_list, deserialize_identity, single_deserializer, list_deserializer"
     )
-    writer.write("from typing import cast, Type")
+    writer.write("from typing import Final, Type")
     writer.write(f"LAYER = {tl.layer!r}")
     writer.write(
-        "TYPE_MAPPING = {t.constructor_id(): t for t in cast(tuple[Type[Serializable]], ("
+        "TYPE_MAPPING: Final[dict[int, Type[Serializable]]] = {t.constructor_id(): t for t in ("
     )
     for name in sorted(generated_type_names):
         writer.write(f"  types.{name},")
-    writer.write("))}")
+    writer.write(")}")
     writer.write("RESPONSE_MAPPING = {")
     for functiondef in tl.functiondefs:
         writer.write(