diff --git a/asgiref/timeout.py b/asgiref/timeout.py
index d3fbca8b..6e5086f4 100644
--- a/asgiref/timeout.py
+++ b/asgiref/timeout.py
@@ -7,6 +7,7 @@
 
 
 import asyncio
+import warnings
 from types import TracebackType
 from typing import Any, Optional, Type
 
@@ -35,6 +36,10 @@ def __init__(
         self._timeout = timeout
         if loop is None:
             loop = asyncio.get_running_loop()
+        else:
+            warnings.warn(
+                """The loop argument to timeout() is deprecated.""", DeprecationWarning
+            )
         self._loop = loop
         self._task = None  # type: Optional[asyncio.Task[Any]]
         self._cancelled = False