diff --git a/CHANGES/274.misc b/CHANGES/274.misc
new file mode 100644
index 0000000..4e2e6db
--- /dev/null
+++ b/CHANGES/274.misc
@@ -0,0 +1 @@
+Improve type annotations for `__exit__` and `__aexit__` methods.
diff --git a/async_timeout/__init__.py b/async_timeout/__init__.py
index e5b2caa..26c50c2 100644
--- a/async_timeout/__init__.py
+++ b/async_timeout/__init__.py
@@ -109,9 +109,9 @@ def __enter__(self) -> "Timeout":
 
     def __exit__(
         self,
-        exc_type: Type[BaseException],
-        exc_val: BaseException,
-        exc_tb: TracebackType,
+        exc_type: Optional[Type[BaseException]],
+        exc_val: Optional[BaseException],
+        exc_tb: Optional[TracebackType],
     ) -> Optional[bool]:
         self._do_exit(exc_type)
         return None
@@ -122,9 +122,9 @@ async def __aenter__(self) -> "Timeout":
 
     async def __aexit__(
         self,
-        exc_type: Type[BaseException],
-        exc_val: BaseException,
-        exc_tb: TracebackType,
+        exc_type: Optional[Type[BaseException]],
+        exc_val: Optional[BaseException],
+        exc_tb: Optional[TracebackType],
     ) -> Optional[bool]:
         self._do_exit(exc_type)
         return None
@@ -206,7 +206,7 @@ def _do_enter(self) -> None:
         self._state = _State.ENTER
         self._reschedule()
 
-    def _do_exit(self, exc_type: Type[BaseException]) -> None:
+    def _do_exit(self, exc_type: Optional[Type[BaseException]]) -> None:
         if exc_type is asyncio.CancelledError and self._state == _State.TIMEOUT:
             self._timeout_handler = None
             raise asyncio.TimeoutError