diff --git a/docs/topics/jobs.rst b/docs/topics/jobs.rst
index 769925dd5..8d6b2458b 100644
--- a/docs/topics/jobs.rst
+++ b/docs/topics/jobs.rst
@@ -104,6 +104,15 @@ If you wish to log the requests that couldn't be serialized, you can set the
 :setting:`SCHEDULER_DEBUG` setting to ``True`` in the project's settings page.
 It is ``False`` by default.
 
+.. note:: Because requests are serialized with :mod:`pickle`, the objects you
+    store on a request, such as the values of its
+    :attr:`~scrapy.Request.cb_kwargs` and :attr:`~scrapy.Request.meta`
+    dictionaries, are deep-copied when the request is written to and later read
+    back from the job directory. As a result, the callback receives a *copy* of
+    those objects rather than the original ones, and changes made to the copy are
+    not reflected in the original object. Keep this in mind if you rely on
+    sharing mutable state through ``cb_kwargs`` or ``meta``.
+
 .. _job-dir-contents:
 
 Job directory contents
diff --git a/docs/topics/request-response.rst b/docs/topics/request-response.rst
index a0fff6acb..67b435067 100644
--- a/docs/topics/request-response.rst
+++ b/docs/topics/request-response.rst
@@ -188,6 +188,13 @@ Request objects
         ``failure.request.cb_kwargs`` in the request's errback. For more information,
         see :ref:`errback-cb_kwargs`.
 
+        .. note:: When :setting:`JOBDIR` is set, requests are serialized to disk
+            with :mod:`pickle` (see :ref:`request-serialization`). As a result,
+            the callback receives a deep copy of any object stored in
+            ``cb_kwargs``, so mutating such an object in the callback does not
+            affect the original. Avoid relying on shared mutable state passed
+            through ``cb_kwargs`` in that case.
+
     .. attribute:: Request.meta
        :value: {}